I have a house that was built in 1984. The roof trusses are constructed from wood that is 34mm (1 3/8") by 95mm (3 3/4"). I have no idea what the rating of the wood is. Each truss is spaced about 600mm (centre to centre) apart. The ceiling joist part of the truss spans 7.2 metres. Some of the wood has been spliced together using what looks like perforated metal sheets banged into each side of the wooden beams. The roof trusses are of a W type, fink, construction.
I want to partly board the roof area using Knauf spaceboard (chipboard with polyfoam insulation underneath) so that It can be effectively used for storage.
Where can I find information about the load carrying capacity for my roof space? Something like kg/m2?
There are intermediate stud walls, which hopefully give support. There is also a cold water tank (up there) that supplies my hot water cylinder in the airing cupboard in the bathroom. It is supported by two wooden beams laid across 4 of the ceiling joists. Doesn't seem to have caused a problem.
It is probably going to be ok for what I want, I just like to have all of the relevant information.
They are W "Warren" braced. Ultimate breaking strain probably around 2-5 tons on any given beam. Unacceptable deflection? probably a fair bit less. Probably half a ton on any beam. Adding a chipboard floor to spread the load will probably result in a floor not much worse than any normal room.
I think you will find that the supports for the tank span a small room such as a bathroom. This room's walls will be taking the strain.
And to be even more brutal, the laws concerning cross bracing were changed at about that time so your present roof might not be up to modern standards. Do you know what kind of cross bracing you have and what modern standards are for that type of roof?
Perhaps someone on here will point out to us what these standards are these days.
I can't find any reference to the figures above in the truss searches I've done to date - do you have a reference perhaps?
I've been watching this thread with interest, as next week we move into a
70s bungalow with a very similar roof structure. Our trusses are spanning
7.7 metres, and made up from the same 95x35 timber. The only real difference is that our trusses are on a slightly narrower 500mm spacing. There are internal block walls under most of the trusses, but interestingly at one end of the building there is a 3 metre section with no support - and no apparent ceiling bowing. There is an existing water tank, sitting on 100x50 timbers nailed(!) to the vertical members, parallel to three of the truss bases, at about a foot up - presumably to gain a little extra head. This is only partly over an internal wall, and does not seem to have distorted the structure - although I need to check this more carefully once we are in.
Our new neighbours (who have been there some twenty years) have boarded out their loft, and store a fair bit of "stuff", and say they have had no problems to date.
I would like to add extra insulation to the 100mm or so that is there now, and was thinking of adding parallel joists above the present bases of the trusses, to give space for another 150mm of glass fibre. These joists would be something like 100 or 125x35m, sitting on blocks on the wall plates, and bolted to the truss vertical(ish) members. The centre of each joist would have to have a bolted joint, as 7.5 metre timber is (obviously) difficult to get, and impossible to get into the roof space anyway. I could then board out the centre 3.5m or so for access and storage.
My rough calculations seem to show that the cost of the timber & glass fibre would be a bit less than the equivalent insulation value of Kingspan or similar, and the timber/glass combination would make subsequent access to services easier in the future. I would also assume that effectively doubling the truss bases, albeit at a slightly higher level, should make the ceiling/loft floor more rigid.
Has anyone done anything like this to date, or have any thoughts?
"Charles Fearnley" wrote in message news:zY_Sh.9143$ snipped-for-privacy@text.news.blueyonder.co.uk...
I have a similar style loft with 95mm x 35mm timbers. I screwed lengths of
95x35 onto the timbers first before boarding so the existing 100m insulation was not comprimised. Also spend time and effort getting 8'x2' sheets of flooring board in the loft rather than the expensive B&Q "loft floor packs" as its much cheaper and considerably quicker.
Also a good excuse to get yourself some new power tools to play with as flooring is much quicker with one drill with say 4mm drill for screw holes, another for countersink and an electric screw driver to screw down.
Oh also last chance to get down the stud walls to get access to mains (or to lighting ring) to put some handy mains sockets in the loft for aerial amps etc.
Nope. Just that I have lifted a tin on similar unsupported beam sizes over a similar span.
Well the one way yo brace a loft floor that really works is to bolt verticals - BOLT - between the rafters and the joists...its not as rigid as warren bracing, but its a lot better than nowt.
Wood is a lot stronger then people think, its juts very elastic, and most regulations are in the light of unacceptable deflections rather than collapse.
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