New garage help

28 Aug 2021
Reaction score
United Kingdom
Hi all, as you can likely see I am newbie on here. I am a very confident DIY’er, having previously spent several years on the tools.

I am currently in the early stages of a garage/workshop build. I have (in my mind) the design I want. In simple terms the block work footprint will be roughly 7.7x6.7, overall height just under 4m. Having discussed this with my bricky he is suggesting a cavity wall (75mm) with some kind of medium to light density block. He also said this would negate the need for any internal piers given the long runs on block work.

The roof will be a simply dual pitch and will run left to right on 7.7m elevation. Having checked all local council planning documents it would appear this is possible with just regs.

I have designed and built previously at home myself, and did so with a large timber building within another part of property. I am keen to do the same with this, if I can. I have a very good friend who is a superb bricky and he is lined up for all ground works and block work. I will undertake all roof timber myself. I am still not sure on the final finish on the roof. (Either slate or metal panels)

I am keen to keep it with 4m overall height for a few reasons, one being retaining my own views from upstairs widows. But, I also however want to maximise all space within the structure by having a vaulted roof. I am confident spanning an RSJ from gable to gable would achieve this, along with the ability to use a block and tackle to maybe lift engines from cars etc. (Max load 500kgs). My initial thoughts either birds-mouthing the 6x2 rafters in to both the wall plate and RSJ. The ridge beam sitting the RSJ. I figured I’d need to make some OSB gussets to reinforce the join between both side, would doing this being enough to negate the structural integrity that roof joists offer?
My intention on the roof thereafter would be rafter spacing at 24” and clad competely with 18mm osb. Initially this will just be covered in normal shed felt - I haven’t yet decided if I want slate to match the house or black corrugated sheets.

Can anyone suggest what size of RSJ would be sufficient? Accounting for 6x2/18mm OSB, 500kgs max lift on a RSJ mounted hoist, and maybe a dash of on snow on the roof?

In addition, the main door for this long term will likely be a roller door. The structural opening will be approx 2850 (keeping within a 3m door as they measure). The lintel for this, I thought I could use a fairly conventional cavity lintel, would this be ok at near on 3m span taking one course of blocks on both sides and the roof rafters directly above? I know block work normal distributes weight, one course this won’t happen.

Last question, I am on heavy clay soil, there are trees within a few meters of the build. They’re all well trimmed. We are torn as to the best footings. On paper conventional 1m footings looks fine. The trees however add a layer of complexity and my bricky has suggest a raft may be better. Having tried to do a roughy calculation the amount of concrete overall concrete for both they seem to need the same. Which would be best?

Thanks in advance for any help.
Sponsored Links
You might need to consider a rsj over the opening rather than just a lintel. Many manufacturers say you need more blockwork over the lintel in order for it to be stable - over such a span you might have issues with a roller doors tolerances otherwise.

Might be cheaper to do a 100mm cavity thermally.
Just be careful that no part of the building is less than 2m from any boundary- if it is you're down to 2.5 height without pp.
You'll need a surprisingly chunky RSJ to support a 500kg live load at centre span- you'd be better off with a set of shear legs and leave the roof doing roof things.
I used a Birtley lintel above my 3m roller shutter (on a single apex 9 degree pitched roof)- BCO was happy with it, been there 5 years now & not moved. With my door the mech is all supported by the frames up the sides of the opening so all the lintel is doing is holding the blocks and roof up.
Founds- I'd go trench myself & pour the floor once the walls are up or at dpc, avoids all the design sweat in a raft. Talk to BCO- they'll give you a steer.
Thanks for the replies, regards to the boundary lines, I’m am on just under an acre of land so thankfully have no issues there.

The lintel for the roller door I have looked in to further and found this:
It seems to be what I need and can be spec’d in most cavity sizes. Also has built in Dpc, which actually looks like it could work

Removing the need for the overhead RSJ to carry any load beyond the roof structure any ideas what I should be looking at? Will the wall being cavity be enough to withstand the fact there will be no roof joists linking front to back?

I am again leaning more towards conventional footings. Much easier to order concrete for too lol
Sponsored Links
You usually tie the gable ends to the 3 nearest rafters (nogged as well,)- use the same straps as you will for retaining the wall plates. The ridge beam shouldn't be under tension, it's main job is to provide stability and an easy way of fixing the rafter ends so doesn't have to be anything massive (at 7700 you might actually find it cheaper to get a bit of steel)
You'll need something tieing the bottom ends of the rafters together (so the roof doesn't spread). Whatever you use will be in tension so again nothing massive unless you plan on storing stuff up there

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local