Loft trussed roof ideas

[katar83]

Before I go to a structural engineer, I thought I'd ask some questions here.

I just finished boarding up the loft which of course took ages to do(30+ hours). Earlier this year I've installed the velux window which helped massively with this job. Of course this is a crappy trussed roof and the loft is only going to be used as storage but I had this idea of removing the centre webs and fitting a triangular/angle shaped ridge beam, with rafters screwed in and tied to it and the beam sitting on a small lintel on the internal wall to spread the load, flush with the rafters and supporting the whole roof at the top. I'd keep the end webs which sit against each internal wall and just remove the four centre ones on each side(they are ~58cm apart) This would make the whole loft much more usable and I wouldn't hit my head on them so often.

Bracing everything for the job would be easy, I just wanna know if this is a sound idea. The beam would be ~3.5 meters long only so nothing too crazy, its a semi detached house.

PS

There doesn't seem to be much weight sitting on these middle long webs, that I want to remove, they are quite sloppy right now but the short ones that I do want to keep are definitely tight, under tension and holding a lot of weight.

 

[stevie888]

DO NOT DO IT,

 

[katar83]

DO NOT DO IT,

Might need bit more than that. Do not go to structural engineer?

 

[noseall]

Before I go to a structural engineer, I thought I'd ask some questions here.

I just finished boarding up the loft which of course took ages to do(30+ hours). Earlier this year I've installed the velux window which helped massively with this job. Of course this is a crappy trussed roof and the loft is only going to be used as storage but I had this idea of removing the centre webs and fitting a triangular/angle shaped ridge beam, with rafters screwed in and tied to it and the beam sitting on a small lintel on the internal wall to spread the load, flush with the rafters and supporting the whole roof at the top. I'd keep the end webs which sit against each internal wall and just remove the four centre ones on each side(they are ~58cm apart) This would make the whole loft much more usable and I wouldn't hit my head on them so often.

Bracing everything for the job would be easy, I just wanna know if this is a sound idea. The beam would be ~3.5 meters long only so nothing too crazy, its a semi detached house.

PS

There doesn't seem to be much weight sitting on these middle long webs, that I want to remove, they are quite sloppy right now but the short ones that I do want to keep are definitely tight, under tension and holding a lot of weight.

Did you get SE advice on the Velux install? I can't see any bracing either. Have you removed any?

 

[Dereekoo]

There doesn't seem to be much weight sitting on these middle long webs, that I want to remove, they are quite sloppy right now but the short ones that I do want to keep are definitely tight, under tension and holding a lot of weight.

Perhaps things may redistribute when you get the design snow load on the roof (75kg/m2 standard) which will then double or more the load that the current concrete tiles give (40 -80kg/m2) and the "lot of weight" becomes a lot lotter. I should imagine a SE will run a mile if asked to look at your vision.

 

[stevie888]

Might need bit more than that. Do not go to structural engineer?

I missed the fact that you'd already butchered one to put a Velux in.

Trusses are actually incredibly flimsy things: they are computer designed to the absolute minimum and rely on every individual component being in place. If a member wasn't necessary for structure, it wouldn't be there!

It is perfectly feasible to do a loft conversion in a trussed roof, but it's a lot harder and therefore more costly than a traditional cut and pitched roof which usually has a nice load bearing wall somewhere, You would need a proper SE design or alternately use Telebeams.

As Dereekoo suggests, most SE's will be less than impressed by your vision.

 

[katar83]

Did you get SE advice on the Velux install? I can't see any bracing either. Have you removed any?

I didn't. Bracing is there, adjoining trusses were strengthened. No need to worry about Velux.

I'm well aware, that with e.g. snow there would be significantly more load in there and they would most likely stiffen up.
Telebeams from what I understand are mainly there for proper conversions where I would remove the whole web sections and have far more things supported on the floor joists which this isn't obviously the case with this modification, here I would be removing less than half of them only(leaving the outer ones and wall ones) and transferring the load from that half - four individual inner webs sitting on the floor joists(that are part of these trusses) to a steel beam sitting on the internal wall. Steel beam would obviously be significantly stronger, would brace the structure better and offer exactly the same point of support as the centre webs do right now for the top of the truss. The only thing changing would be that section support, from floor joists to internal wall.
This obviously aint a typical "conversion" and I'm aware that normally everyone that looks at these trusses immediately thinks the whole house will collapse the moment you swing a hammer and nail at them but being an engineer(although not a structural one!) it kinda works in my head and I would need an SE or someone knowledgeable and open minded to ideally tell me why this wouldn't so I can sleep better hence a question here and me thinking of finding an SE to actually look into it and do some calculations.
Hope that makes sense!

 

[HERTS P&D]

Bracing is there, adjoining trusses were strengthened.

Can you post pictures of the bracing.

Andy

 

[katar83]

There's a diagonal bracing just where the lower left corner of the velux is and there's a horizontal one tying the outer webs. They are there and this wasn't what I asked about. The same ones are on the other side of the roof and there's one at the top of the roof that is nailed to all trusses and technically attached by a metal band to the internal wall but its only holding by hopes and dreams and effectively not tied at all, thanks to great skill of local 90s workforce. This is another reason why I think a steel beam would make this actually stronger as could fix that issue too at the same time.

 

[freddiemercurystwin]

Speak to a proactive SE, if you can find one, the brief being that the trusses remain solely for the purposes of creating the roof space and storing not much more than some Xmas decs and a fat plumber fixing the boiler, strictly speaking you do need Building Control Approval and any surveyor inspecting your house when you come to sell will (or should) question what's gone on so expect some grief then and some buyers will run a mile even if you have some SE number crunching paperwork to prove it works as is intended.

Really, having lived in a house with trussed roof used for storage myself, I can't see the point, unless you have money to burn.

 

[Dereekoo]

You could assume the rafters are normal rafters supported with a central beam and see what the calcs throw up re BM and deflection. Width ,depth and span required and dead load of tiles and if those short braces actually rest on a supporting wall below assume they act as a purlin this reducing span of rafters

 

[katar83]

Thanks, that at least gives me something to go with to an engineer, finding one is another matter, they are rarer than hens teeth here it seems so might have to look further away. The short webs where they join the bottom of the whole truss do sit on a supporting bedrooms/bathroom walls, they are just internal framed walls but still a supporting structure I guess. I did not think about that.

The whole idea about the loft is to indeed just keep it as storage space at the sides, for christmas decorations, and fat me sitting on a bean bag in the middle and looking through a telescope, also insulating the loft which is now done and roof with a bit of celotex to keep the rest of the house warmer in winter/cooler in summer. Velux is also there to eventually provide more light in the dark single window living room downstairs as I want to put one of these walk on glass panels in the loft floor, between the trusses, directly over stairs which sit at the bottom of the living room below Velux.

If this modification to the roof worked and was confirmed by SE as sound it would be relatively cheap to do I imagine, custom steel beams aren't that expensive, paperwork might be but it ain't a deal breaker. It would annoy me less for sure as I'm quite tall and they are always in the way.

 

[chickenlips]

You would be better off going to the company that has manufactured the trusses and asking them if what you want to do is possible. There is a tag on the apex plate of the truss, that will tell you where they are from. Contact them before seeking a SE, most SE's will not touch trussed roof remedials.

I'd also guess the work you have already done will probably fail likely on the plates, if checked by the truss manufacturer. If an opening was to be designed in to the roof, there would be 2-ply trusses either side of that velux, so that's also something to bear in mind

 

[Munroast]

There doesn't seem to be much weight sitting on these middle long webs, that I want to remove, they are quite sloppy right now but the short ones that I do want to keep are definitely tight, under tension and holding a lot of weight.

they will momentarily go in and out of tension when its windy, if you remove them your roof may collapse on a stormy night

and if by some miracle it doesn't, if you ever try and sell the buyers surveyor will say to them - don't buy that its roof could blow off

 

[freddiemercurystwin]

Well not wanting to play devils advocate here (I've already said it may prove problematic when he comes to sell) but if an SE proves it works (or some version of the OP's utopia) and the modifications are carried out as necessary then the roof won't blow off or fail.

It's pointless speaking to the truss manufacturer, especially for some ancient roof, they won't be the slightest bit interested furthermore they're not structural engineers and will always outsource to a separate structural engineer for anything out of the ordinary anyway.