20 foot roof span options?

boatbuilder

Hi,

I have started building a 20 foot by 40 foot garage building and want to have an upstairs in it as well. I've built it like a dwelling house so far...cavity wall and all that and I'm intending to do a slated roof.

I'm wondering where to go with the roof though, as the entire downstairs is one open space with no supporting walls in the middle. Will <SNIP> be good enough to span the 20 feet? Any ideas how to frame the roof / floor?

I'm a woodwork teacher so you'd think I know this stuff......:eek:

sas

My garage that is under construction is 22 ft by 30 ft. Same build as yourself. Mine is 1.5 storey

Rather than running the timber across the 22ft span, we are putting RSJ across the span at 10ft and 20ft from the front i.e at 1/3 and 2/3 along the 30ft length of the garage.

The floor joists for upstairs will then run from front to back in approx 10ft lenght sitting into the web of the RSJs.

Steel is pretty cheap at the moment so this isn't a pricey option.

As regards the roof, what I have discussed with the engineer is the following:
1. The course beneath the wall plate along the side walls of the garage will be done using a u-block.
2. A box steel piece will run along the inner leaf of the front and rear walls. This steel will pass through a notch in the u-blocks and into the centre of the u-blocks. A plate will have been welded onto these box steels at each end.
3. Then concrete will be poured in the u-blocks which will fill around the plates on the box steel holding them in place.

In the end you have a fully tied ring beam. The u-blocks will be directly beneath the eaves so bridging the cavity there is no problem. The box steel won't bridge the cavity on the front and rear gables so no issue there.

I hope I've described my self clearly.

Good luck,

SAS

cork2

<SNIP>put a beam down the centre or the garage and cut your joists into the web of it. <SNIP> as for roofing you can do something similiar. build two beams into the gable end blockwork. fasten a <SNIP> to the top of each beam birdsbeak your rafters onto them and use them as you purlins.

Poor Uncle Tom

Please take a few minutes to familiarise yourself with the rules of the Forum.

On construction related matters any specifying of structural components is prohibited. Any queries in this regard need to be dealt with by an architect/engineer privately.

The above is taken from the forum charter and applies to all three of you. The next person that requires editing on this thread gets banned.

boatbuilder

Ok sorry, I should have read the rules.

One last question (which I hope is ok as it is a general question)

Is it worth considering prefabricated roof trusses as a one stop solution to a wide-span situation like this, considering I want a "room in the roof" as well? Maybe cost would be prohibitive?

Thank you and I hope this question is ok.

Poor Uncle Tom

This questing is fine and worth getting a price on although I think you will find that standard construction with engineer designed steel supporting beams will probably work out most economical.

martin46585

hi there, i just completed a similar roof on a garage 6.0mts between the wallplates.
i went with trusses which were cantilevered out over the wallplates to give xtra length to joist which in turn give xtra height.
you wont acheive 2.4mt to the collars unless your pitch is fairly steep,
but you will get 2mt which is enough for storage if this is your intention.
cost will be fairly similiar to cut roof without the steel rsjs.

boatbuilder

Thanks.

I like the sound of trusses which would avoid the use of steel and would take less time and effort to put up.

Leadership

I no nothing about roof construction but I know my VW's. Than van in the picture looks sweet!

boatbuilder

Yeah I sold her a while ago unfortunately.....I miss her -(