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Loft conversion joists
A quick play with SuperBeam appears to indicates for my proposed loft
conversion floor (4m span, 2kN/m2, 500mm spacing), I need either: 1. Timber joists (220 x 50) (CL16) 2. Flitch joists (147 x 50) (10mm plate, not full depth) 3. Steel joists (127 x 76). (UB 13mm thickness Grade 43) Given that the steel joists would save 70mm of height, propelling the project into feasibility, why aren't all loft conversions done with them? Furthermore, the calculated deflection ended up as 3.4mm rather than 11mm, so it would be less bouncy. A quick phone up of the local steel merchants gave me the chance to sound all professional by reeling off the SuperBeam specifications (they seemed to know what I was saying!) and gave me a total cost of around 700 quid plus VAT to joist out a 8m by 4m total area, making the cost only a small proportion of a loft conversion anyway. It's not like the timber would have been free, either. Is there something preventing the use of steel for joists? I realise that they need to be fireproofed, but this can't be that expensive can it? Isn't the fireproofing just squirty foam? Christian. P.S. By not restricting to standard sized UBs, further fiddling shows that a 76 x 76 x 12mm RSJ section would also suffice, giving a clear 144mm clearance over the wood. In fact, slightly less, as this RSJ would actually fit within the current thickness of the 4" ceiling joists. Coupled with installed an unventilated roof (as per Kingspan's recommendation) with 75mm between joists, 25mm underneath and no ventilation space, I would only lose 25mm of headroom. Not bad for a building regs compliant conversion, don't you think? What's the catch? |
Loft conversion joists
In article , Christian
McArdle wrote: A quick play with SuperBeam appears to indicates for my proposed loft conversion floor (4m span, 2kN/m2, 500mm spacing), I need either: 1. Timber joists (220 x 50) (CL16) 2. Flitch joists (147 x 50) (10mm plate, not full depth) 3. Steel joists (127 x 76). (UB 13mm thickness Grade 43) Given that the steel joists would save 70mm of height, propelling the project into feasibility, why aren't all loft conversions done with them? Furthermore, the calculated deflection ended up as 3.4mm rather than 11mm, so it would be less bouncy. A quick phone up of the local steel merchants gave me the chance to sound all professional by reeling off the SuperBeam specifications (they seemed to know what I was saying!) and gave me a total cost of around 700 quid plus VAT to joist out a 8m by 4m total area, making the cost only a small proportion of a loft conversion anyway. It's not like the timber would have been free, either. Is there something preventing the use of steel for joists? I realise that they need to be fireproofed, but this can't be that expensive can it? Isn't the fireproofing just squirty foam? Excellent choice of software g - though I get a deflection for the timber of 9mm - it's a load-sharing system. As your key question, I think it's a matter of timber being a much more friendly material to work with, especially in the confines of a loft. How do you hold up the ends of these joists: once you get into fabrication then the cost goes up appreciably. Also the fire proofing is probably going to involve more than squirty foam: I'm not up on the details but intumescent paint is not cheap and has pretty rigid application specifications. -- Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm |
Loft conversion joists
"Christian McArdle" wrote in message et... A quick play with SuperBeam appears to indicates for my proposed loft conversion floor (4m span, 2kN/m2, 500mm spacing), I need either: 1. Timber joists (220 x 50) (CL16) 2. Flitch joists (147 x 50) (10mm plate, not full depth) 3. Steel joists (127 x 76). (UB 13mm thickness Grade 43) Given that the steel joists would save 70mm of height, propelling the project into feasibility, why aren't all loft conversions done with them? Furthermore, the calculated deflection ended up as 3.4mm rather than 11mm, so it would be less bouncy. A quick phone up of the local steel merchants gave me the chance to sound all professional by reeling off the SuperBeam specifications (they seemed to know what I was saying!) and gave me a total cost of around 700 quid plus VAT to joist out a 8m by 4m total area, making the cost only a small proportion of a loft conversion anyway. It's not like the timber would have been free, either. Is there something preventing the use of steel for joists? I realise that they need to be fireproofed, but this can't be that expensive can it? Isn't the fireproofing just squirty foam? Christian. P.S. By not restricting to standard sized UBs, further fiddling shows that a 76 x 76 x 12mm RSJ section would also suffice, giving a clear 144mm clearance over the wood. In fact, slightly less, as this RSJ would actually fit within the current thickness of the 4" ceiling joists. Coupled with installed an unventilated roof (as per Kingspan's recommendation) with 75mm between joists, 25mm underneath and no ventilation space, I would only lose 25mm of headroom. Not bad for a building regs compliant conversion, don't you think? What's the catch? Don't use steel RSJs in a loft conversion. This is total overkill. Use Masonite "I" beams. http://www.masonite-beams.se If height is problem then you can double them up. |
Loft conversion joists
Excellent choice of software g - though I get a deflection for the
timber of 9mm - it's a load-sharing system. I am but a novice. I simply modelled a single beam with 1kN per metre distributed over the length. This is based on 2 joists per meter and 2kN loading/m2. As your key question, I think it's a matter of timber being a much more friendly material to work with, especially in the confines of a loft. How do you hold up the ends of these joists: I sort of presumed they sat on top of the walls with the aid of whatever bearing structures are normally used. The main "fabrication" would be how to incorporate the stairs. However, only the top landing is problematic here. A bit of ASCII art: -----4m---- ----4m----- -1m- ########################### ^ # # | # | #------------# +----# 1m # # | # | #------------#-------+----# \/ # # # #------------#------------# # # # #------------#------------# # # # #------------#------------# ## = structural wall -- = steel joist | = trimmer joist As you can see, only one part is problematic. The 4m joists (or centre supported 8m) lay on brickwork at the ends. Where the stairs come up, it will be sufficient to just stop at the centre wall. However, a landing needs to be incorporated into the end where the missing joist section is. The landing is bounded by one untrimmed joist on one side, and structural brickwork on two sides. I presume the solution will be to use a trimmer joist or suchlike. I wouldn't be surprised if a timber structure would be appropriate here. What do you think? BTW, the roof needs redoing at the same time anyway, so the slates will be off when the joists are craned into position. The old roofing system will be replaced by an unventilated Kingspan system. Christian. P.S. You seem to know a lot about loft conversions, what are my chances of the foundations needing underpinning before all this can be done? House built 1909. Christian. |
Loft conversion joists
Don't use steel RSJs in a loft conversion. This is total overkill. Use
Masonite "I" beams. http://www.masonite-beams.se Their smallest is 200mm deep, which is too great. I'd might as well use 220mm timber. I'm really looking for sub 100mm, so it fits inside the existing ceiling joists. Headroom is everything. I'm willing to pay 10 times as much as a simple timber solution to bring down the depth. Christian. |
Loft conversion joists
"Christian McArdle" wrote in message et... A quick play with SuperBeam appears to indicates for my proposed loft conversion floor (4m span, 2kN/m2, 500mm spacing), I need either: 1. Timber joists (220 x 50) (CL16) 2. Flitch joists (147 x 50) (10mm plate, not full depth) 3. Steel joists (127 x 76). (UB 13mm thickness Grade 43) Given that the steel joists would save 70mm of height, propelling the project into feasibility, why aren't all loft conversions done with them? Furthermore, the calculated deflection ended up as 3.4mm rather than 11mm, so it would be less bouncy. A quick phone up of the local steel merchants gave me the chance to sound all professional by reeling off the SuperBeam specifications (they seemed to know what I was saying!) and gave me a total cost of around 700 quid plus VAT to joist out a 8m by 4m total area, making the cost only a small proportion of a loft conversion anyway. It's not like the timber would have been free, either. Is there something preventing the use of steel for joists? I realise that they need to be fireproofed, but this can't be that expensive can it? Isn't the fireproofing just squirty foam? you also have to allow for a method of attaching the flooring to the steel when I looked into this for my loft I found the best method of saving the most headroom was to span steel beams with wood inserts across the longest length, and suspend wooden joist from them |
Loft conversion joists
In article ,
Christian McArdle wrote: Don't use steel RSJs in a loft conversion. This is total overkill. Use Masonite "I" beams. http://www.masonite-beams.se Their smallest is 200mm deep, which is too great. I'd might as well use 220mm timber. I'm really looking for sub 100mm, so it fits inside the existing ceiling joists. Headroom is everything. I'm willing to pay 10 times as much as a simple timber solution to bring down the depth. I'm planning a loft conversion and am considering composite wooden I-beam joists which are 9" deep by 2" wide. See an earlier post, but basically they are light, come in up to 50' lengths and only require 600mm between each joist - the suppliers also do the design which keeps the BCO happy. I'm hanging mine from the wall plate that the current ceiling joists and roof rafters are attached. But my ceiling need to be replaced anyway. This way I gain 3" of head space. Can you describe your roofing system and cost. It seems just what I'm after - I was considering using the warm roof insulation battens available from Screwfix. Neil |
Loft conversion joists
when I looked into this for my loft I found the best method of saving
the most headroom was to span steel beams with wood inserts across the longest length, and suspend wooden joist from them I'm not sure I quite get this. Could you explain in more detail? Would a simple floating T&G floor be sufficient? Is there any need to attach the floor to the joists? Christian. |
Loft conversion joists
Can you describe your roofing system and cost. It seems just what I'm
after - I was considering using the warm roof insulation battens available from Screwfix. Firstly, it requires the entire roof covering, battens and felt (if present) to be removed. It isn't a simple retrofit job. Basically, it can't be done with the conventional roofing felt in place. The breathable sarking membrane is ESSENTIAL to allow the wooden rafters to remain dry. --------+------------+----------- Slates/tiles --------+------------+----------- ################################# Battening ## Counter battening ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Breathable sarking membrane ----+----+----------------------- | | |R'tr| Kingspan Thermapitch 75mm Insulation + Rafters | | TP10 zero ODP ----+----+----------------------- Kingspan Thermawall TW56 zero ODP 25mm Insulation --------------------------------- --------------------------------- 12.5mm Plasterboard See http://www.insulation.kingspan.com/newdiv/pdf/tp10.pdf Unventilated Insulation Between & under rafters Figure 1a The battens can be replaced by 18mm sarking board (with a slight reordering of components), although in my case, that would sink the roofline below neighbouring properties. Good for newbuild or detached properties, though. Also, if the rafters are 100mm, you can just get away with building regulations for loft conversions (but not new build) filling only between rafters, although 25mm underneath is better to avoid cold bridging and condensation, as well as improved energy efficiency. Christian. |
Loft conversion joists
Christian McArdle wrote:
A quick play with SuperBeam appears to indicates for my proposed loft conversion floor (4m span, 2kN/m2, 500mm spacing), I need either: You can probably use a loading of 0.8kN / m rather than 1kN/m Note also that a floor is a load sharing system which reduces the size requirements a bit more. 1. Timber joists (220 x 50) (CL16) Taking the above comments into consideration you could use something like 150x75 C24 so that saves you 70mm as well. Given that the steel joists would save 70mm of height, propelling the project into feasibility, why aren't all loft conversions done with them? Because it is a pain to work with. When you want to trim a bit of here or there it is not just a quick cut with a saw. Fixing other beams to stringers is not as simple as nailing on a joist hanger with square twist nails! Also not as easy if you need to drill a hole through the centre of a joist for a pipe or wire run. Furthermore, the calculated deflection ended up as 3.4mm rather than 11mm, so it would be less bouncy. True - but even 10mm is not that bouncy. If you need to go to steel at all - then looking at flitch beams first, gives more "workability". Most of the advantages of working with wood, and you are still in the bounds of manually handling the beams without needing a crane (you can lug the three bits up a ladder separately and assemble the beam in the loft). A quick phone up of the local steel merchants gave me the chance to sound all professional by reeling off the SuperBeam specifications (they seemed to know what I was saying!) and gave me a total cost of around 700 quid plus VAT to joist out a 8m by 4m total area, making the cost only a small proportion of a loft conversion anyway. It's not like the timber would have been free, either. Timber will cost you as much in all likelihood. The floor joists cost me something in the order of 500 quid for the wood, and 400 for the flitch plates (I used four) plus all the hangers, bolts, dogs etc. Having said that I saved on the cost of a crane! -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
when I looked into this for my loft I found the best method of
saving the most headroom was to span steel beams with wood inserts across the longest length, and suspend wooden joist from them I'm not sure I quite get this. Could you explain in more detail? span a steel beam, say 8x5, either side above the ceiling/roof joists below bolt 6 x 2 joist inside the full length of the beams (you'll have to drill the beam or buy one ready drilled) and attach joist hangers to it then suspend the new floor joist from the hangers the beauty of this method is you can set the floor height to anything you like (within reason) by placing the joists between the ceiling/roof joists below Would a simple floating T&G floor be sufficient? Is there any need to attach the floor to the joists? wouldn't a T&G floor would come apart if it's not secured ? |
Loft conversion joists
Christian McArdle wrote:
Also, if the rafters are 100mm, you can just get away with building regulations for loft conversions (but not new build) filling only between rafters, although 25mm underneath is better to avoid cold bridging and condensation, as well as improved energy efficiency. With 4" rafters, if you are not stripping the whole roof, and, the existing under tile felt is not breathable, then you can get away with : Tiles Felt 2" gap 2" PIR foam between rafters 25 or 30mm foam underneath plasterboard However you will need to arrange for ventilation at the soffits and ridge of the roof. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
span a steel beam, say 8x5, either side above the ceiling/roof joists
below bolt 6 x 2 joist inside the full length of the beams (you'll have to drill the beam or buy one ready drilled) and attach joist hangers to it then suspend the new floor joist from the hangers the beauty of this method is you can set the floor height to anything you like (within reason) by placing the joists between the ceiling/roof joists below I simply don't see how this would work for me. Where do you hide the 8" (200mm) beam? I only have 100mm to play with and need a continuous floor with the conventional joist length being a centre supported 8m. wouldn't a T&G floor would come apart if it's not secured ? I presume you use PVA, like old style non-click laminate. I don't know if you're allowed a floating floor of this size. The actual floor size would be more like 6.5m x 4m, as there would be a dwarf wall at the front non-dormer end. Thick skirting to hide the expansion gap and some blobs of low modulus silicone to stop the entire floor migrating to one end. Is this allowed? Christian. |
Loft conversion joists
In article , Christian
McArdle wrote: Their smallest is 200mm deep, which is too great. I'd might as well use 220mm timber. I'm really looking for sub 100mm, so it fits inside the existing ceiling joists. Headroom is everything. I'm willing to pay 10 times as much as a simple timber solution to bring down the depth. [for sci.eng.civil this relates to providing new floor joists in a house loft conversion, 4m span, 500mm c/s, domestic floor load only] On a quick check a 90x90x3.6mm hot-finished SHS (square hollow section) Grade S355 (Grade 43) steel would do the job and weighs only 9.6kg/m. IIRC Screwfix do self drilling chipboard decking screws to go into steel, so decking it out would be easy. You'd need to check out the fireproofing carefully: I suspect it would come to intumescent coating by the supplier with any damage made good on site. I've cross-posted this to sci.eng.civil to see whether any of the engineers there can see any good reason why square tube cannot be used in this situation. -- Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm |
Loft conversion joists
25 or 30mm foam underneath
From memory, don't you need 50mm underneath? You need around 100mm Kingspan/Celotex to get to loft conversion standards, don't you? Christian. |
Loft conversion joists
Taking the above comments into consideration you could use something
like 150x75 C24 so that saves you 70mm as well. Then then, the 76mm RSJ that it later came up with saves me a whopping 120mm (the existing 4" joists limit the saving to this value). This is no idle matter. Headroom is one of the possible no-go reasons on the conversion (the other main worry being foundations). Every 10mm is an enormous saving. Because it is a pain to work with. When you want to trim a bit of here or there it is not just a quick cut with a saw. Fixing other beams to stringers is not as simple as nailing on a joist hanger with square twist nails! OK. How do you hang a steel joist? Does it lie on top, is it bolted down, can you just use joist hangers a la timber. Also not as easy if you need to drill a hole through the centre of a joist for a pipe or wire run. The 76mm RSJ gives me 24mm between the laths of the old ceiling and the bottom of the steel, assuming the top of the steel is flush with the existing ceiling joists. True - but even 10mm is not that bouncy. If you need to go to steel at all - then looking at flitch beams first, gives more "workability". Well, the flitch beam gave me 150mm, which is a vast improvement. I wonder if you can convert a steel beam into a "decorative" flitch by calculating it entirely on steel strength with some wood bolted on to have something to screw to? of the advantages of working with wood, and you are still in the bounds of manually handling the beams without needing a crane (you can lug the three bits up a ladder separately and assemble the beam in the loft). I'm sure it wouldn't take long to get 20 4m steel beams into position, would it? Crane hire for a day can't be that bad. Front access is excellent, unlike the rear. Timber will cost you as much in all likelihood. The floor joists cost me something in the order of 500 quid for the wood, and 400 for the flitch plates (I used four) plus all the hangers, bolts, dogs etc. Having said that I saved on the cost of a crane! Bloody hell. I though the wood would be a fraction of that. I never bothered to calculate it. How much can a little crane or hoist cost to hire for the day? 250 quid? Also, I bet the 76x76x12 RSJ is probably not much more than half the 127x75x13 UB in weight and cost. Christian. |
Loft conversion joists
On a quick check a 90x90x3.6mm hot-finished SHS (square hollow section)
Grade S355 (Grade 43) steel would do the job and weighs only 9.6kg/m. I've just tried it in SuperBeam, and I'm happy with that! At 40kg a beam, you could carry them up the stairs with a few mates! I bet a square section would be really easy to work with, too. It also reduces worries in terms of foundation strength. I'd need about 20 of these beams and 800kg doesn't sound that scary. I had thought about the self drilling screws (I'm using them in my conservatory), but assumed that the beam sections would be too thick for them. My only concern is a possible point load when it comes to redesigning the roof bracing that might require a vertical column to support a purlin. However, this could easily be accomodated by hanging a much larger beam at that point and not bothering to attach the floorboards to that one. (i.e. a 90x90x5 SHS). I have no idea of how to calculate the roof structure to determine the magnitude of the point load. For all I know, the purlin will just be replaced by a steel beam itself and not require further bracing to the floor. You'd need to check out the fireproofing carefully: I suspect it would come to intumescent coating by the supplier with any damage made good on site. Any idea how much an intumescent coating would cost? Is it significantly more (i.e. triple). I bet the 90x90x3.6 SHS would cost peanuts uncoated. Christian. |
Loft conversion joists
In article , Christian
McArdle wrote: I simply don't see how this would work for me. Where do you hide the 8" (200mm) beam? I only have 100mm to play with and need a continuous floor with the conventional joist length being a centre supported 8m. /\ / \ / \ / \ / \ / \ / \ / \ / \ A D B E C You're planning to put your joists from A-B and B-C and holding up the roof some other way. Most loft conversions I designed in my earlier life had serious steel beams at D and E spanning from party wall to party/flank wall: these supported the floor joists which now only have span D-B and B-E also the dwarf partitions that help hold up the roof. -- Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm |
Loft conversion joists
On a quick check a 90x90x3.6mm hot-finished SHS (square hollow section)
Grade S355 (Grade 43) steel would do the job and weighs only 9.6kg/m. P.S. I bet it is much easier to weld trimmer joists into the landing space, too, even if the wall thickness might need beefing up from the stairs point load and the missing joist. Christian. |
Loft conversion joists
In article , Christian
McArdle wrote: Also, I bet the 76x76x12 RSJ is probably not much more than half the 127x75x13 UB in weight and cost. The last number is the nominal weight: one is 12kg/m run, the second 13kg. So I'd expect them to cost about the same. Availability of RSJ section might be an issue too, although they are listed in the 'Blue Book' -- Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm |
Loft conversion joists
In article ,
Christian McArdle wrote: Can you describe your roofing system and cost. It seems just what I'm after - I was considering using the warm roof insulation battens available from Screwfix. Firstly, it requires the entire roof covering, battens and felt (if present) to be removed. It isn't a simple retrofit job. Basically, it can't be done with the conventional roofing felt in place. The breathable sarking membrane is ESSENTIAL to allow the wooden rafters to remain dry. --------+------------+----------- Slates/tiles --------+------------+----------- ################################# Battening ## Counter battening ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Breathable sarking membrane ----+----+----------------------- | | |R'tr| Kingspan Thermapitch 75mm Insulation + Rafters | | TP10 zero ODP ----+----+----------------------- Kingspan Thermawall TW56 zero ODP 25mm Insulation --------------------------------- --------------------------------- 12.5mm Plasterboard See http://www.insulation.kingspan.com/newdiv/pdf/tp10.pdf I am stripping the roof. Do I need the counter battens. Counter battens may raise my roof tiles above my neighbours since I'm in an end terrace. Cheers, Neil |
Loft conversion joists
You're planning to put your joists from A-B and B-C and holding up the
roof some other way. Most loft conversions I designed in my earlier life had serious steel beams at D and E spanning from party wall to party/flank wall: these supported the floor joists which now only have span D-B and B-E also the dwarf partitions that help hold up the roof. I see now. This could possibly work for me at the front. However, the back is planned to be a full dormer extension, so this wouldn't work there. I'd prefer the floor to extend from A-D for storage purposes, although a lip from a beam would be no great concern. Unfortunately, the BC joist still needs to span the distance, without the E beam, so it doesn't solve the rear problem. Would you still recommend hanging the front joists off a 'D' beam, or would it be more economic to just span the lot and build the partition across the joists? Note that an escape window will almost certainly be required that will probably require floor space forward of the beam. I want at least some light storage space in front of the beam, including a compartment in the escape window "tunnel" to hold a rope ladder and other safety equipment. One additional complication is a full height bay window at the front of the property. This could cause problems finding somewhere for those joists to hang from. Obviously I can have a beam of any height at that point, provided that the joists can hang with its bottom in the same space and not sit on top. This is effectively the 'D' beam solution moved so the beam is at the front edge of the wall, but using steel joists, rather than wood to span the gap. However, is it possible to hang or weld steel joists off a beam in the same way as timber? / / - rafter '' / / stud partition -- '' / / '' / /+----+ '' -- |beam| -- weld/joist hanger? '' ##| +--------------------------------------++----- ##| | 90x90x3.6 SHS Joist || #####+----+--------------------------------------++----- ------------------------------------------------+--+---- p/b | | bay masonry wall - | | extension | | (existing wood ceiling joists not shown for clarity Christian. |
Loft conversion joists
Also, I bet the 76x76x12 RSJ is probably not much more than half the
127x75x13 UB in weight and cost. The last number is the nominal weight: one is 12kg/m run, Oh. I thought it was thickness of the base material. Are there any UB sections less than 100mm? SuperBeam shows none, although I do like your SHS idea as being easier to work with in terms of fabrication around the stairway. Am I right in saying this is an advantage that applies? Is it allowed to weld trimmer joists into place? Would this section be better done in wood? I presume wood sections can be kept down to 100mm depth when talking about 1m spans. ################### | # | # +------------# | # SPL-| # -----+------------# # # = load bearing wall - = joists | = trimmer joist + = weld SPL = stair/newel post point load Christian. |
Loft conversion joists
I am stripping the roof. Do I need the counter battens. Counter battens
may raise my roof tiles above my neighbours since I'm in an end terrace. I don't believe so, although I'm only going on what I read in the link. It basically seems to be saying that if you want to use battens, then the sarking membrane goes under them. If you want to use a sheet of plywood instead, then the membrane goes above (presumably to protect the plywood, which would otherwise be at risk, unlike battens, which would drain off onto the membrane pretty easily and be ventilated). Christian. |
Loft conversion joists
neil
which supplier did you find that does the design of the ibeam as well ? I have a 7 M span cheers larry "Niel A. Farrow" wrote in message ... In article , Christian McArdle wrote: Don't use steel RSJs in a loft conversion. This is total overkill. Use Masonite "I" beams. http://www.masonite-beams.se Their smallest is 200mm deep, which is too great. I'd might as well use 220mm timber. I'm really looking for sub 100mm, so it fits inside the existing ceiling joists. Headroom is everything. I'm willing to pay 10 times as much as a simple timber solution to bring down the depth. I'm planning a loft conversion and am considering composite wooden I-beam joists which are 9" deep by 2" wide. See an earlier post, but basically they are light, come in up to 50' lengths and only require 600mm between each joist - the suppliers also do the design which keeps the BCO happy. I'm hanging mine from the wall plate that the current ceiling joists and roof rafters are attached. But my ceiling need to be replaced anyway. This way I gain 3" of head space. Can you describe your roofing system and cost. It seems just what I'm after - I was considering using the warm roof insulation battens available from Screwfix. Neil |
Loft conversion joists
"Christian McArdle" wrote in message et... Don't use steel RSJs in a loft conversion. This is total overkill. Use Masonite "I" beams. http://www.masonite-beams.se Their smallest is 200mm deep, which is too great. I'd might as well use 220mm timber. I'm really looking for sub 100mm, so it fits inside the existing ceiling joists. Headroom is everything. I'm willing to pay 10 times as much as a simple timber solution to bring down the depth. TJI do shallower beams. |
Loft conversion joists
Christian McArdle wrote:
25 or 30mm foam underneath From memory, don't you need 50mm underneath? You need around 100mm Kingspan/Celotex to get to loft conversion standards, don't you? Nope, 75 - 80mm should be fine... I put 50+30mm in total on ours, and the BCO passed it yesterday ;-)) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
"Christian McArdle" wrote in message et... Can you describe your roofing system and cost. It seems just what I'm after - I was considering using the warm roof insulation battens available from Screwfix. Firstly, it requires the entire roof covering, battens and felt (if present) to be removed. It isn't a simple retrofit job. Basically, it can't be done with the conventional roofing felt in place. The breathable sarking membrane is ESSENTIAL to allow the wooden rafters to remain dry. --------+------------+----------- Slates/tiles --------+------------+----------- ################################# Battening ## Counter battening ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Breathable sarking membrane ----+----+----------------------- | | |R'tr| Kingspan Thermapitch 75mm Insulation + Rafters | | TP10 zero ODP ----+----+----------------------- Kingspan Thermawall TW56 zero ODP 25mm Insulation --------------------------------- --------------------------------- 12.5mm Plasterboard If you want 12.5mm more height, you can get the 25mm insulation with paper rather than foil covering and then plaster skim this. |
Loft conversion joists
"Christian McArdle" wrote in message et... 25 or 30mm foam underneath From memory, don't you need 50mm underneath? You need around 100mm Kingspan/Celotex to get to loft conversion standards, don't you? Yes and no. There is a get-out clause which allows a U of 0.3 for conversions. But I'd still agree your proposed way is better. |
Loft conversion joists
"Christian McArdle" wrote in message et... On a quick check a 90x90x3.6mm hot-finished SHS (square hollow section) Grade S355 (Grade 43) steel would do the job and weighs only 9.6kg/m. I've just tried it in SuperBeam, and I'm happy with that! At 40kg a beam, you could carry them up the stairs with a few mates! I bet a square section would be really easy to work with, too. It also reduces worries in terms of foundation strength. I'd need about 20 of these beams and 800kg doesn't sound that scary. How does that weight sound to your walls though ? Mine would definitely object. |
Loft conversion joists
"Christian McArdle" wrote in message et... when I looked into this for my loft I found the best method of saving the most headroom was to span steel beams with wood inserts across the longest length, and suspend wooden joist from them I'm not sure I quite get this. Could you explain in more detail? Would a simple floating T&G floor be sufficient? Is there any need to attach the floor to the joists? There was a Grand Designs where they glued the floor to steel beams. I remember it because the glue didn't stick. |
Loft conversion joists
Christian McArdle wrote:
Would you still recommend hanging the front joists off a 'D' beam, or would it be more economic to just span the lot and build the partition across the joists? Note that an escape window will almost certainly be required that will probably require floor space forward of the beam. I want at least some light storage space in front of the beam, including a compartment in the escape window "tunnel" to hold a rope ladder and other safety equipment. Sounds a bit like what I did... Not a stunning picture, but you may be able to see what is going on. The dwarf wall replaces the function of the purlin to the front. The space from the wall to the eves will become cupboard space. http://www.internode.co.uk/temp/dwarf.jpg You should be able to make out beam F at the back of the cupboard space http://www.internode.co.uk/temp/beam-layout.gif thisflys over the existing ceiling joists (which hold up a bonnet roof over the bay window). The main floor joists are then hung below this beam on long hangers. I presume similar could be done even if the floor joists are SHS rather than timber. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
Christian McArdle wrote:
Timber will cost you as much in all likelihood. The floor joists cost me something in the order of 500 quid for the wood, and 400 for the flitch plates (I used four) plus all the hangers, bolts, dogs etc. Having said that I saved on the cost of a crane! Bloody hell. I though the wood would be a fraction of that. I never bothered In fact having just looked back at my running total spreadsheet, it was less. My first order for wood was about 350. That also included the roof joists for the dormer, and some 4x2 for studwork. Hence the floor beams may only have been 200 of that. If you need to use C24 that also puts theprice up a bit, and in our case meant it took about a week to get it all ordered and delivered. C16 could have been done from stock probably. The steel for the flitch plates was not that expensive - probably about 200 ish (and that included drilling and painting with a passivated finish). The expensive things were all the little bits like shoes, hangers, bolts, dogs etc. They added another 250. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
John
It seems that you have a lot of knowledge regarding loft conversions. I am soon to move into a new house and intend to convert the loft. Would you be able to offer me advice on the job, it will be strictly DIY! Thanks Andrew |
Loft conversion joists
Andrew Barnes wrote:
John It seems that you have a lot of knowledge regarding loft conversions. I am soon to move into a new house and intend to convert the loft. Would you be able to offer me advice on the job, it will be strictly DIY! I am happy to share what I have learned. I don't claim to be any kind of expert, since my actual experiance of doing loft conversions now runs to a grand total of one! Needless to say yours may be somewhat different. As I am now nearing the end of my project I hope I have encountered most of the issues that need to be dealt with along the way. Perhaps when the project is complete, I will knock up a web site covering the process, if there is enough interest. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
Andrew Barnes wrote:
It seems that you have a lot of knowledge regarding loft conversions. I am soon to move into a new house and intend to convert the loft. Would you be able to offer me advice on the job, it will be strictly DIY! Yup I am happy to share what I have learned. I don't claim to be any kind of expert, since my actual experiance of doing loft conversions now runs to a total of one! Needless to say yours may be somewhat different. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Loft conversion joists
In article ,
el pee wrote: neil which supplier did you find that does the design of the ibeam as well ? I have a 7 M span I got some names from a glulam beam trade assoc - don't have it to hand (did a web search). Sent 3 of them my requirements last week but haven't heard anything yet. In the mean time I've found a local structural eng. who is doing the beam calc. for £40. With his info I can then directly get sizes for metal or wood. Neil |
Loft conversion joists
I put 50+30mm in total on ours, and the BCO passed it yesterday ;-))
A quick check of the tables shows you're right. The 50+30mm of insulation is absolutely right on the nail for 0.3. 75mm wouldn't have done it. The problem come when you install between rafters only. They publish figures for 75mm and 100mm, with the 75mm being well out at 0.36, but the 100mm being well in at 0.28. My intended roof (75mm between and 25mm underneath) gives 0.25. Christian. |
Loft conversion joists
If you want 12.5mm more height, you can get the 25mm insulation with paper
rather than foil covering and then plaster skim this. I haven't heard of this. Is there a brand name for this product? Sounds just the thing. Christian. |
Loft conversion joists
thisflys over the existing ceiling joists (which hold up a bonnet roof
over the bay window). The main floor joists are then hung below this beam on long hangers. I presume similar could be done even if the floor joists are SHS rather than timber. Yes, that looks similar to my proposed solution, although on a grander scale and with the stairs in a different location. Has anyone got a definitive answer as to whether the steel joists can be "hung" off the structural beam and how? Christian. |
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