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House built in 1995 with typical fink truss roof, spanning 8.5m.
The bottom chord is only 75 x 38mm. I'd like to board the loft for storage and initially thought of using those plastic risers to clear the 270mm insulation (plus air gap). However, that feels like I'd be creating some potentially problematic point loading on these rather tiny rafters.
I'd don't want to go silly with stuff up there but the we've already got some separated plasterboard from the chap doing a recent boiler service.
What's the best way to strengthen things up there?
Trussed roofs are designed to go on quickly and cheaply and are difficult to alter afterwards without affecting the roof covering or ceilings.
How you would go about changing them depends on the nature of the trusses.
If they’re cranked trusses (you have a section of sloping ceiling before the flat section) I’d leave well alone as you’d have to strengthen the cranked section of the rafters and your entering structural engineer territory.
If the bottom cords are spanning wall to wall you can supplement the cord by positioning additional timbers next to the cord and bolting through (There are plenty of span tables to give you a better idea of the section size you need). Unfortunately given the nature of the trusses you are never going to get full length (wall to wall timber) into position without taking areas of the roof covering off (which might be the cheapest/quickest way to do it if you are serious).
If you are aiming to do it DIY you would have to build up beams laminate style which requires you to achieve minimum overlaps at joints, the right type & number of fixing etc which again strictly speaking is structural engineering territory.
Watching with interest...
I've got a 6x6m garage with the same timber size trusses. Would be really useful if I could use the whole roof space for storage (all that stuff you want to keep but rarely use/seasonal stuff) but the impression I get is that I can't really cheaply do anything. I was wondering how much it would cost to just whip the whole roof off and rebuild with something more substantial. It sounds like the first step in any case is a structural engineer?
Cheers.
Each side has one tension and one compression web so there's no chance of getting any really long lengths up there.
Was wondering if I'd be better building up each chord sistered to the original or whether two layers of perpendicular timbers might be better.
I don't want to add so much weight in timber that I don't actually gain any strength.
Guess next question should be, how much does a structural engineer cost?
Guess next question should be, how much does a structural engineer cost?
Not a lot in my experience, £150 ish for something simple like this.
Sorry Onzadog, full on thread hijack here, will an architect perform structural engineering calculations? Google searches round my way seem to through up mainly Commercial/Industrial types (Aberdeen). Any tips on who I could solicit to give me some good objective advice on the most cost effective solution? My options as I see them are:
- Live with what I've got (spending thousands to save money not throwing stuff out seems daft)
- Reinforce existing trusses and board out roof space
- Completely re-roof garage with beefier trusses
- extend another bay on the garage
I'm not sure how likely I am to throw money at it right now so I'd not really want to waste anyone's time (happy paying for a consultaition but I'd not be confident there'd be follow up work soon). I'd been unsure who'd be best to approach, builder, architect or structural engineer.
Mat I'll fire you the name of the folk I used on Facebook.
Came up from stonehaven . Chap I used to work with at alpine.
Came up listened to me and threw out some radical ideas at varying degrees of cost.
I actually went with one of their ideas in the end and work starts Monday after a covid delay.
They got my structural calcs done by their pet engineer.
Sounds good, thanks Terry!
Onzadog, the whole truss is the load bearing unit. You can't increase the capacity just by doubling the bottom chord; the load in the bracing, connections and rafters will increase as well. If you want to use the loft for storage, you need to put floor joists independent of the rafter, and span them between the supporting walls.
Mat, in Scotland you need structural calculations to be certified by an SER registered engineer, who will be a civil or structural engineer, not an architect.