mrbig
Part of things
Semi-professional Procrastinator
Posts: 461
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Jan 28, 2022 18:29:07 GMT
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Been in my current house about 6 years and I’ve been meaning for about 7 of those to look at fitting a 4 post parking lift  As so many of these threads go: is it feasible to remove 3 of these trusses (total of 10) in order to make space for a lift? Obviously the strength will need to be restored somehow but my knowledge doesn’t extend this far! Also, as an aside, the bottom chords are 75x35mm. Can I board it for storage and walk around on it to put stuff up there or will the strength not be sufficient. I only store light stuff up there: car covers, sledges, step ladder, trailer lighting board etc. I've seen figures banded around of anything from 25kg/m2 to 100kg/m2. Is there a formula for doing the calculations somewhere? Thanks in advance good people. [a href="  |https://thumbsnap.com/wC1dn8d5"] |https://thumbsnap.com/wC1dn8d5[/a] |
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1969 German Look Beetle - in progress
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Badger
Part of things
Posts: 250
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Jan 28, 2022 19:32:55 GMT
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I'm guessing you mean remove the central triangular section and the bottom part?
What's the pitch between the trusses? Looks fairly large so I'd be very wary about removing any part of that structure without first reinforcing it significantly.
Have you got more pictures? It's kind of hard to get a handle on the overall roof construction.
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Jan 28, 2022 22:06:53 GMT
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I wouldn’t be removing trusses without first speaking to a structural engineer on the matter
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By eye I would say if you start removing trusses you are going to need a steel ridge beam from gable to gable. Those trusses are already spaced at what appears to be the absolute maximum they could get away with, I certainly wouldn't want to impose any more load from anywhere on them.
You need a structural engineer to come up with a safe method of doing it but don't be surprised if it essential end up with pitching a new roof. In which case you may as well spec it for a decent floor up there along with aging a couple of velux windows for extra light or pitched roof dormers if you want more space.
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Refer to NZS 3604 (timber framed buildings not requiring specific engineering design) or the equivalent British Standard to see what the legalities are. Be aware that 3604 is written for dummies so the member sizes given therein have a huge idiot factor. In reality one can usually get away with a lot less but don't forget to allow for snow loading. Council building inspector mate reckoned that specific engineering design often results in smaller member sizes and therefore less expense than using 3604. He also said that often the difference in cost more than covers the engineer's fee.
Disclaimer, I'm only an engineer's draughtsman, not an actual engineer, but I have built many things for myself none of which have suffered catastrophic collapse even after decades of use.
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Garage Roof Truss Questions…slater
@slater
Club Retro Rides Member 78
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Jan 29, 2022 10:00:40 GMT
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I think you could board it for light weight storage ok but certainly don't go removing truss members.
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Jan 29, 2022 10:58:15 GMT
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I wouldn’t be removing trusses without first speaking to a structural engineer on the matter My first, and only thought, is don't do anything before consulting a structural engineer. That does not include someone who works out the calculations on the back of a fag packet either. Playing about with roof structures first off will likely bring you to the attention of the local Building-Inspectors. Secondly it could well negate any house-insurance, which your mortgage company require. Just be extremely careful; hindsight is a wonderful thing. |
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16grit
Part of things
Posts: 213
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Jan 29, 2022 14:25:57 GMT
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Have a google on 'room in the roof trusses' and take a read of what pops up. Might give you some ideas as to how the space might be reworked in safety.
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Jan 29, 2022 16:00:07 GMT
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I have a very similar roof in my garage and i've plasterboarded the underside and then insulated above.
I then put some timber across parallel to the trusses on one side of the roof (I used CLS studwork) and put some chipboard on this for storage. The studwork reinforces each truss to the others and provides space for the 100mm of insulation so its not compressed.
I only store very light things up there (xmas decorations, pasting table, a few mostly empty tins of house paint. If you wanted to store anything heavy up there I would look to install some form of steel coal posts in the garage below to take the load.
As mentioned above doing anything to a roof, especially one like this needs expert advise otherwise you could have a huge weight of tiles joining you in the garage on top of you or your pride and joy.
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Jan 29, 2022 22:32:03 GMT
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Hi,
As a former truss designer I can advise a bit.
Trusses generally have a 250n/m2 storage load. Normally you’d only up that if it was a attic truss or specifically requested.
35x72 generally is the smallest TR26 (timber grade) used in truss fabrication so it’s unlikely to have any additional load.
If the trusses are relatively new (last 20 odd years) they may have a tag on with a fabricator and job number. If you can find this the supplier may be able to offer more information.
If the spacing is to be increased you’d need to either run that through the truss software to see if the trusses change (I’d expect the timber sizes to go up one size and possibly nail plate sizes may change) or get an engineer to look at it. A good old school engineer would tell you how to strengthen with timber scabs and ply gussets. I’d expect you’d need to double them up either side to create a 1m gap and put a purlin at the ridge and ideally half way down to split the rafter span (if you wanted to keep the same rafter sizes.
Other thing you could do is send a sketch to a truss company and ask for a quote pretending it’s a new roof with the 1m gap and see what results they come back with for comparison. They should send you a layout with a profile and timber sizes if you ask for it.
Hope that makes sense!
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Jan 29, 2022 22:33:29 GMT
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Sorry, should have said.
As above, do not cut any members out. These are designed to be as economical as possible. Especially for the mass house builders. Any cutting of the members is like to cause a failure.
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Jan 29, 2022 23:33:50 GMT
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I was thinking about this on my dog walk, if it had 2 gable ends or a gable and into the house, I suspect as suggested above you could get away with adding 1 or more purlins each side and possibly a glue/ laminate beam under the ridge. A structural engineer who does loft conversions should be able to suggest the easiest/ most cost effective way.
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Last Edit: Jan 29, 2022 23:35:52 GMT by dodgerover
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Jan 30, 2022 20:01:24 GMT
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You could also get a steel frame made up to go inside basically a A frame for each end and steel purlins and ridge as above.
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