Home |
Search |
Today's Posts |
|
UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
I am planning on insulating my loft to the recommended 270mm, and would
also like to lay floorboards above the insulation so I can keep using the loft for storage. The gap between the ceiling and the top of the existing joists is 70mm, so there's 200mm to go. I'm intending on adding two strips of 40 x 100 on top of the existing joists, screwing them down, and laying the insulation between them and boards on top. It seems like a fairly simple job. There's one bit of information I'm missing; what sort of timber would be appropriate for this job? Dave |
#2
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Dave Page wrote:
I am planning on insulating my loft to the recommended 270mm, and would also like to lay floorboards above the insulation so I can keep using the loft for storage. The gap between the ceiling and the top of the existing joists is 70mm, so there's 200mm to go. I'm intending on adding two strips of 40 x 100 on top of the existing joists, screwing them down, and laying the insulation between them and boards on top. It seems like a fairly simple job. When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. So you'd be better off fitting the new joists perpendicular to the originals I'd have thought. However, your original ceiling joists are not very meaty, so depending on the span, you may have a problem there, if you are going to pile lots of new joists, floorboards and storage items up there. There's one bit of information I'm missing; what sort of timber would be appropriate for this job? Just bog standard timber joists from the timber yard - haven't a clue what species it is! David |
#3
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Lobster wrote:
When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I was intending to replace the existing insulation - it's only about an inch thick, dead old (over 10 years), and patchily installed. Plus insulation seems to come (from Wickes at least, who are selling rolls ad near-half-price until this weekend) in 170mm and 100mm depths. So you'd be better off fitting the new joists perpendicular to the originals I'd have thought. However, your original ceiling joists are not very meaty, so depending on the span, you may have a problem there, if you are going to pile lots of new joists, floorboards and storage items up there. The joists are 14" / 355mm apart, so there are plenty of them (this is particularly annoying since insulation roll seems to come in 400mm widths). The thought of laying new joists crosswise is interesting, not least because it would save me a few screws. As it was, I'm not planning on putting too much weight up there, and was considering only raising every other joist to save on timber. On the other hand, the loft hatch is only 750mm wide, so if I want the boards to be supported by three joists, I'll need to space the joists at roughly 350mm anyway There's one bit of information I'm missing; what sort of timber would be appropriate for this job? Just bog standard timber joists from the timber yard - haven't a clue what species it is! That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m lengths, I'll ask someone at the store whether it's suitable for my purposes if it works out cheaper than a timber merchant. Dave |
#4
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Lobster wrote:
When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) |
#5
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
The Natural Philosopher wrote:
Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) Umm, no. Perpendicular can also mean simply "a straight line at right angles to another line". |
#6
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Ian Stirling wrote:
The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) Umm, no. Perpendicular can also mean simply "a straight line at right angles to another line". ....that is laying horizontal. Orthogonal is better. Less implications of verticality., |
#7
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
The Natural Philosopher wrote:
Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. After all, laying insulation foam vertically wouldn't make sense. Dave |
#8
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Dave Page wrote:
Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I was intending to replace the existing insulation - it's only about an inch thick, dead old (over 10 years), and patchily installed. Plus insulation seems to come (from Wickes at least, who are selling rolls ad near-half-price until this weekend) in 170mm and 100mm depths. I wouldn't bother lifting the old stuff - 'orrible job, and it won't do any harm being added to by what you're going to lay on top. I've used the Wickes stuff; it's still intended to be laid perpendicularly (or orthogonally - FFS!) even if you're starting from scratch (I think their instruction sheet says so). There's one bit of information I'm missing; what sort of timber would be appropriate for this job? Just bog standard timber joists from the timber yard - haven't a clue what species it is! That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m lengths, I'll ask someone at the store whether it's suitable for my purposes if it works out cheaper than a timber merchant. That's just the job, their 'kiln-dried', unfinished stuff is what you want, with the purple sticker! Look down its length to check it's straight before you put it on your trolley; especially if they haven't got much stock in, a lot of it can be banana-shaped. Personally, I find Wickes cheaper than timber yards as they won't give me decent trade prices. Still not too happy about your weight issue though, but I could be wrong - hopefully someone with more knowledge than me will comment? David |
#9
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
In article ,
Dave Page wrote: The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. After all, laying insulation foam vertically wouldn't make sense. 'Perpendicular' without the sense of vertical makes no sense at all. What would it be hanging (-pend-) from? -- John Cartmell john@ followed by finnybank.com 0845 006 8822 Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com Qercus - the best guide to RISC OS computing |
#10
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Dave Page wrote:
The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. Ah, but would you have understood if I'd said "orthogonal"? :-) David |
#11
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Lobster wrote:
Dave Page wrote: I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. Ah, but would you have understood if I'd said "orthogonal"? :-) Probably, yes. Or even "crossways". Dave |
#12
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"John Cartmell" wrote in message ... In article , Dave Page wrote: The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. After all, laying insulation foam vertically wouldn't make sense. 'Perpendicular' without the sense of vertical makes no sense at all. What would it be hanging (-pend-) from? Yes it does. It only implies vertical in some of its meanings (architecture, physical landscape) and not in others (maths and the conjunction of two lines or planes). A quote from Round the World in Eighty Days: "It was supplied with two rows of seats, perpendicular to the direction of the train on either side of an aisle which conducted to the front and rear platforms." Orthogonal could just as easily be vertical or horizontal as well. Of course one could have used "at right angles to" ) -- Bob Mannix (anti-spam is as easy as 1-2-3 - not) |
#13
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
In article ,
Lobster wrote: Dave Page wrote: The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. Ah, but would you have understood if I'd said "orthogonal"? :-) As a board game designer - yes! I use it in practically every set of rules that I produce ... ... but feel obliged to define it every time! ;-) -- John Cartmell john@ followed by finnybank.com 0845 006 8822 Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com Qercus - the best guide to RISC OS computing |
#14
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Dave Page wrote:
The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. After all, laying insulation foam vertically wouldn't make sense. It would - but it tends to slide off I'm wondering ATM if any of the common '270mm' rolls of stuff on the market can be split into 3 or 4 parts - for insulating the garage. |
#15
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Lobster wrote:
Dave Page wrote: I was intending to replace the existing insulation - it's only about an inch thick, dead old (over 10 years), and patchily installed. Plus insulation seems to come (from Wickes at least, who are selling rolls ad near-half-price until this weekend) in 170mm and 100mm depths. I wouldn't bother lifting the old stuff - 'orrible job, and it won't do any harm being added to by what you're going to lay on top. Frankly, it's all I can do to stop it blowing away in a draft. I've used the Wickes stuff; it's still intended to be laid perpendicularly (or orthogonally - FFS!) even if you're starting from scratch (I think their instruction sheet says so). Fair enough. In that case, I'm not sure what the best thing to do is; if I lay the insulation perpendicular to the existing joists, I'm not going to be able to get 270mm down over the existing joints (or a little way either side) unless I lay *more* joisting over the top. Seems the best thing to do might be to lay down the 100mm rolls *between* the existing joists, lay another 200mm of joisting perpendicular to that (squishing down some of the insulation beneath), and rolling the 170mm insulation between the new joisting. Still not too happy about your weight issue though, but I could be wrong - hopefully someone with more knowledge than me will comment? Well, if there's concern, I'll hold off for a little while until consensus forms. Can't wait too long though, I want to make the purchase before the Wickes special offer on insulation ends on Saturday, and I'm busy all day Friday. Dave |
#16
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"John Cartmell" wrote in message ... In article , Bob Mannix wrote: "John Cartmell" wrote in message ... In article , Dave Page wrote: The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. After all, laying insulation foam vertically wouldn't make sense. 'Perpendicular' without the sense of vertical makes no sense at all. What would it be hanging (-pend-) from? Yes it does. It only implies vertical in some of its meanings (architecture, physical landscape) and not in others (maths and the conjunction of two lines or planes). AFAIK it should only be used in maths & drawing where it's used to represent a physical verticality. Oh no, definitely not - two lines in maths/geometry perpendicular to each other are usually representing no physical reality at all but are always described as perpendicular Where you are describing a physical (3 or more dimensions) situation 'perpendicular' cannot mean horizontal. It cannot *mean* horizontal per se, I agree, but could be used to describe things which form lines at right angles in some arbitrary plane (which might be horizontal) by considering them merely as geometric concepts. If the information being conveyed included information on verticality then perpendicular would clearly mean vertical. A quote from Round the World in Eighty Days: "It was supplied with two rows of seats, perpendicular to the direction of the train on either side of an aisle which conducted to the front and rear platforms." The translator made an error. That one's for a rainy day, I fear, not having a French copy to hand ) -- Bob Mannix (anti-spam is as easy as 1-2-3 - not) |
#17
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
In article , Bob Mannix
wrote: "John Cartmell" wrote in message ... In article , Bob Mannix wrote: "John Cartmell" wrote in message ... In article , Dave Page wrote: The Natural Philosopher wrote: Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I think you mean 'orthogonal' Perpendicular is walls... ;-) I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. After all, laying insulation foam vertically wouldn't make sense. 'Perpendicular' without the sense of vertical makes no sense at all. What would it be hanging (-pend-) from? Yes it does. It only implies vertical in some of its meanings (architecture, physical landscape) and not in others (maths and the conjunction of two lines or planes). AFAIK it should only be used in maths & drawing where it's used to represent a physical verticality. Oh no, definitely not - two lines in maths/geometry perpendicular to each other are usually representing no physical reality at all but are always described as perpendicular No. You have to define the horizontal plane first. Of course that may only be assumed but, if you have assumed a line across the page to be the horizon and the top of the page as up, then a line at right angles to the first line is perpendicular to it *because you have defined the first line as the horizon*. In lazy maths today we generally forget that we have implicitly made that initial assumption. Where you are describing a physical (3 or more dimensions) situation 'perpendicular' cannot mean horizontal. It cannot *mean* horizontal per se, I agree, but could be used to describe things which form lines at right angles in some arbitrary plane (which might be horizontal) by considering them merely as geometric concepts. If the information being conveyed included information on verticality then perpendicular would clearly mean vertical. You can indeed make any arbitrary plane the horizontal plane. In the case in hand you are saying that you have assumed that a vertical plane through the house is the horizontal plane. Can we please return to reality before the thought makes me sea-sick! ;-) A quote from Round the World in Eighty Days: "It was supplied with two rows of seats, perpendicular to the direction of the train on either side of an aisle which conducted to the front and rear platforms." The translator made an error. That one's for a rainy day, I fear, not having a French copy to hand ) http://www.fourmilab.ch/etexts/www/tdm80j/tdm80j.html ;-) -- John Cartmell john@ followed by finnybank.com 0845 006 8822 Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com Qercus - the best guide to RISC OS computing |
#18
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Bob Mannix wrote:
snip Oh no, definitely not - two lines in maths/geometry perpendicular to each other are usually representing no physical reality at all but are always described as perpendicular Normally. |
#19
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Weatherlawyer wrote:
I am planning on insulating my loft to the recommended 270mm, and would also like to lay floorboards above the insulation so I can keep using the loft for storage. The gap between the ceiling and the top of the existing joists is 70mm, so there's 200mm to go. First thing get the cheapest offer you can with the insulation. But for heaven's sake phone around all the other places too first. Builders merchants not only stock it they deiver. Wickes deliver too, for a small fee. I'm not sure where all these "other places" are. I don't know any reputable builder's merchants, and wouldn't know how to tell if one *were* reputable. Wickes was recommended to me by the nice man who did my central heating, and did a very nice job of it too. Secondly, why are you intent on adding timber? If you must walk around up there for maintainance in the future all you need is a walkway built up. If that. You could just lay a plank or two over the wool. As mentioned in my original post: would also like to lay floorboards above the insulation so I can keep using the loft for storage. That's why I'm intent on adding timber Remember there must be a draught in the roof at all times as the amount of moisture that vents through it is quite amazing. Yep, I wasn't going to lay the insulation all the way to the eaves, or to the ceiling. Third: However much you put up there at first, it will have shrunk to a lot less after a few months settlement. Talk it over with the salesmen in the timberyards you get quotes from. They will be far more knowledgeable than staff at Wickes's or similar. Though I must admit a few B&Q staffers I have met seemed on the ball. Bugger, this was the sort of thing I was worried about. Will I need to stick the timber up in the loft for a few months until it adjusts to the weather conditions up there before I can cut and fit it? Dave |
#20
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
In article ,
Ian Stirling wrote: Bob Mannix wrote: snip Oh no, definitely not - two lines in maths/geometry perpendicular to each other are usually representing no physical reality at all but are always described as perpendicular Normally. I do hope that was meant mathematically! ;-) -- John Cartmell john@ followed by finnybank.com 0845 006 8822 Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com Qercus - the best guide to RISC OS computing |
#21
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Dave Page wrote:
Lobster wrote: Dave Page wrote: I understood what Lobster meant, and feel that "perpendicular" was quite appropriate. Ah, but would you have understood if I'd said "orthogonal"? :-) Probably, yes. Or even "crossways". Dave Crossways is good. Plain Builders English. |
#22
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Bob Mannix wrote:
Orthogonal could just as easily be vertical or horizontal as well. Of course one could have used "at right angles to" ) Orthogonal means 'at right angles to' |
#23
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"Dave Page" wrote in message ... Lobster wrote: When topping up old insulation (Rockwool) it's normal and more effective to lay the second layer perpendicular to the first. I was intending to replace the existing insulation - it's only about an inch thick, dead old (over 10 years), and patchily installed. Plus insulation seems to come (from Wickes at least, who are selling rolls ad near-half-price until this weekend) in 170mm and 100mm depths. So you'd be better off fitting the new joists perpendicular to the originals I'd have thought. However, your original ceiling joists are not very meaty, so depending on the span, you may have a problem there, if you are going to pile lots of new joists, floorboards and storage items up there. The joists are 14" / 355mm apart, so there are plenty of them (this is particularly annoying since insulation roll seems to come in 400mm widths). The thought of laying new joists crosswise is interesting, not least because it would save me a few screws. As it was, I'm not planning on putting too much weight up there, and was considering only raising every other joist to save on timber. On the other hand, the loft hatch is only 750mm wide, so if I want the boards to be supported by three joists, I'll need to space the joists at roughly 350mm anyway Lay the joists at right angles and use joist hangers where they meet the walls if any (gable end). Use 6" screws. Unifix supply these quite cheap. Having the at 90 degrees reduces thermal bridging enormously. There's one bit of information I'm missing; what sort of timber would be appropriate for this job? Just bog standard timber joists from the timber yard - haven't a clue what species it is! That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m lengths, I'll ask someone at the store whether it's suitable for my purposes if it works out cheaper than a timber merchant. Dave |
#24
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"Weatherlawyer" wrote in message oups.com... Dave Page wrote: I am planning on insulating my loft to the recommended 270mm, and would also like to lay floorboards above the insulation so I can keep using the loft for storage. The gap between the ceiling and the top of the existing joists is 70mm, so there's 200mm to go. I'm intending on adding two strips of 40 x 100 on top of the existing joists, screwing them down, and laying the insulation between them and boards on top. It seems like a fairly simple job. There's one bit of information I'm missing; what sort of timber would be appropriate for this job? First thing get the cheapest offer you can with the insulation. But for heaven's sake phone around all the other places too first. Builders merchants not only stock it they deiver. Secondly, why are you intent on adding timber? If you must walk around up there for maintainance in the future all you need is a walkway built up. If that. You could just lay a plank or two over the wool. The rolls of insulate come in bags of three, sometimes you have to cut them apart. But if you lay them crosswise over the beams you can lay a full three rolls at a time. Remember there must be a draught in the roof at all times as the amount of moisture that vents through it is quite amazing. As he is removing the old insulation, it is best seal up the holes where cable and pipes penetrate with silicon, then lat a poly vapour barrier on the plasterboard/joist. Pin it with a staple gun to side of the joists and tape the joins with big overlaps. Then lay the insulation and lay the new joists. Then make sure the hatch is sealed and insulated too. |
#25
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Doctor Drivel wrote:
"Dave Page" wrote in message ... Lobster wrote: I was intending to replace the existing insulation - it's only about an inch thick, dead old (over 10 years), and patchily installed. Plus insulation seems to come (from Wickes at least, who are selling rolls ad near-half-price until this weekend) in 170mm and 100mm depths. The joists are 14" / 355mm apart, so there are plenty of them (this is particularly annoying since insulation roll seems to come in 400mm widths). The thought of laying new joists crosswise is interesting, not least because it would save me a few screws. As it was, I'm not planning on putting too much weight up there, and was considering only raising every other joist to save on timber. On the other hand, the loft hatch is only 750mm wide, so if I want the boards to be supported by three joists, I'll need to space the joists at roughly 350mm anyway That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m lengths, I'll ask someone at the store whether it's suitable for my purposes if it works out cheaper than a timber merchant. Dave Lets review the options. 1. Lay new joists on old at 90 degrees This will leave you with a very weak floor, as well as being a pain to insulate. 2. Lay new joists at 90 degrees on joist hangers into the walls This is illegal in a lot of properties under the Party Wall Act, and might get you into a bundle of trouble. 3. Add new 4x2 joists to the top of the old ones, inline, attaching with glue and screws. This is legal, and will bring a dramatic increase in strength to your floor/ceiling structure, enabling you to stack goods to the roof without worry of collapse, distortion, etc. When joining timbers, (since it isnt easy to get a full length one in there) the structure will be stronger if you glue joint them rather than just butt them, but eiher will help. Laying insulation is easy. 4. Add new wood on every other joist This will cause damage to the ceiling, as the differing loads will try to mildly corrugate the non-flexible plaster ceiling. Expect cracking and damage. Any 2x4 will do, as long as its straight. Spruce aka whitewood is cheapest. NT |
#26
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Add new 4x2 joists to the top of the old ones, inline, attaching with glue and screws. This is legal, and will bring a dramatic increase in strength to your floor/ceiling structure, This is a well accepted method when the existing ceiling rafters are already almost deep enough. The aim of gluing and screwing the two parts together is to prevent the composite beam from bending by one part sliding over the other. The glue is much more important than the screws because the large bond area distributes the shear forces more evenly. The main contribution of the screws is to help make a good glue bond, and afterwards they are almost incidental. In loft conversions, this is usually supplemented by glueing and screwing the chipboard floor down, which adds yet more stiffness to the whole structure. -- Ian White |
#27
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
In article
Dave Page wrote: snip As it was, I'm not planning on putting too much weight up there, and was considering only raising every other joist to save on timber. That means the load on the loft floor would only be supported by half of the joists, and the boards would be spanning a considerable gap - neither of these is a good thing. On the other hand, the loft hatch is only 750mm wide, so if I want the boards to be supported by three joists, I'll need to space the joists at roughly 350mm anyway The boards go across the joists, not along them. |
#28
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
In article
Bob Mannix wrote: snip Oh no, definitely not - two lines in maths/geometry perpendicular to each other are usually representing no physical reality at all but are always described as perpendicular I'd have thought 'normal' was the more usual term. |
#29
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Doctor Drivel wrote:
As he is removing the old insulation, it is best seal up the holes where cable and pipes penetrate with silicon, then lat a poly vapour barrier on the plasterboard/joist. Pin it with a staple gun to side of the joists and tape the joins with big overlaps. Then lay the insulation and lay the new joists. Then make sure the hatch is sealed and insulated too. Is that just to stop drafts, or for any other reason? The ceiling appears to be chipboard rather than plasterboard here. Dave |
#31
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"Dave Page" wrote in message ... wrote: Lets review the options. 1. Lay new joists on old at 90 degrees This will leave you with a very weak floor, as well as being a pain to insulate. Hmm, why would this lead to a weak floor? I figured that laying the new joists at 90 degrees to the old ones would spread load across the old joists, and laying the new floorboards across the This method has the advantage that I can space my new joists at 400mm (the pre-cut width of the insulation roll) rather than having to deal with the existing 350mm joist spacing, and means that I can do the loft in fewer "strips" of insulation (three or four as opposed to a dozen). Other people have commented that insulation roll is "supposed" to be laid *across* the joists. I have to assume that this precludes flooring the loft space, and that if I want to floor my loft space, I'll need to lay the roll *along* the joists. Lay insulation between the joists and another layer 90 degrees to that. I have seen a loft floor raised over 1 foot by using short pieces of 4X2. all the same length. These were on end on the existing joists vertically, and secured by small angle pieces. On top on the 4x2s long lengths of 4x2s were laid and 6" screws driven in. These were secured to the gable end wall by joist hangers, which also takes weight off the ceiling. The odd cross brace was inserted so the floor did not wobble, and the chipboard laid on top being well screwed down. The chipboard tightened up the whole floor. MDF was used around the loft hatch, which also added rigidity to the floor too. Easy to do if you have a chop saw and an Impact Driver. This gap was filled with spray-in Warmcell insulation, which also makes the ceiling air-tight too. Warmcell has the equiv performance of Rockwool that is 25% thicker. |
#32
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"Dave Page" wrote in message ... Doctor Drivel wrote: As he is removing the old insulation, it is best seal up the holes where cable and pipes penetrate with silicon, then lat a poly vapour barrier on the plasterboard/joist. Pin it with a staple gun to side of the joists and tape the joins with big overlaps. Then lay the insulation and lay the new joists. Then make sure the hatch is sealed and insulated too. Is that just to stop drafts, or for any other reason? The ceiling appears to be chipboard rather than plasterboard here. About 42% of heat loss in UK homes is via air-leakages. Preventing water vapour from entering the cold loft prevents condensation on the timbers, hence the sealed loft hatch. |
#33
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Doctor Drivel wrote:
Other people have commented that insulation roll is "supposed" to be laid *across* the joists. I have to assume that this precludes flooring the loft space, and that if I want to floor my loft space, I'll need to lay the roll *along* the joists. Lay insulation between the joists and another layer 90 degrees to that. I can't do that without laying the new joists at 90 degrees to the old joists, which I'm told upthread would be a bad idea, or covering the joists. I have seen a loft floor raised over 1 foot by using short pieces of 4X2. all the same length. These were on end on the existing joists vertically, and secured by small angle pieces. Hmm, this sounds like a bigger project in terms of time and complexity than I can budget for at the moment. Nice idea though. Dave |
#34
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
Dave Page wrote:
wrote: Lets review the options. 1. Lay new joists on old at 90 degrees This will leave you with a very weak floor, as well as being a pain to insulate. Hmm, why would this lead to a weak floor? I figured that laying the new joists at 90 degrees to the old ones would spread load across the old joists, and laying the new floorboards across the you'd have exactly the same wood supporting as you have now, and 3" is marginal. Spreading a roomful of load out over a room makes little difference, it only helps with high point loads, not with total load, deflection or rigidity. This method has the advantage that I can space my new joists at 400mm (the pre-cut width of the insulation roll) rather than having to deal with the existing 350mm joist spacing, and means that I can do the loft in fewer "strips" of insulation (three or four as opposed to a dozen). minor in comparison to leaving yourself with a borderline floor support structure. Other people have commented that insulation roll is "supposed" to be laid *across* the joists. I have to assume that this precludes flooring the loft space, thats how its done when theres no flooring. With flooring, the goods themselves will trap air, if packed in cardboard boxes, and so will insulate some more. You can roll insulation out on any unused floored areas if you wish. 3. Add new 4x2 joists to the top of the old ones, inline, attaching with glue and screws. Yeah, this was my original plan, and looks like being what I'll end up doing after all, possibly using the poly vapour barrier mentioned by Doctor Drivel in yes NT |
#35
Posted to uk.d-i-y
|
|||
|
|||
Raising Roof Joists for Loft Flooring
"Dave Page" wrote in message ... Doctor Drivel wrote: Other people have commented that insulation roll is "supposed" to be laid *across* the joists. I have to assume that this precludes flooring the loft space, and that if I want to floor my loft space, I'll need to lay the roll *along* the joists. Lay insulation between the joists and another layer 90 degrees to that. I can't do that without laying the new joists at 90 degrees to the old joists, which I'm told upthread would be a bad idea, It is not. It speads the load and vastly reduces cold bridging. or covering the joists. I have seen a loft floor raised over 1 foot by using short pieces of 4X2. all the same length. These were on end on the existing joists vertically, and secured by small angle pieces. Hmm, this sounds like a bigger project in terms of time and complexity than I can budget for at the moment. Nice idea though. Not expensive to do. Yet the results are well pleasing in many aspects. Dave |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
How much weight could my garage roof joists carry? | UK diy | |||
conflicting advice on roof repair | Home Repair | |||
conflicting advice on roof repair | Home Repair | |||
4" roof joists @ 30cm spacing - planning to board out loft | UK diy | |||
Raising the roof | UK diy |