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?

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

"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.

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.

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.

"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

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

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.

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.

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 |
\================================================= ================/

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 ?

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 |
\================================================= ================/

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.

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

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.

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.

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.

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

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.

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

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

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.

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.

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.

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

"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.

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.

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| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"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.

"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.

"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.

"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.

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.

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| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

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 |
\================================================= ================/

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

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 |
\================================================= ================/

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 |
\================================================= ================/

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

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.

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.

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.