What size wall plate between walls

[Marker121]

Hi I have a small alleyway between my house and garage its 1.5m wide x 4m long i want to box it in and put a flat roof on it

What size timer\wall plates should I use on the walls and should i sit the roof joists on top or use hangers to fasten between? and what do you recommend fastening the plates to the brick walls?

What size roof joists do you recommend, i may add some insulation in the future so I probably need to consider this.

Plan would be use 18 mm OSB and then use EPDM to cover?

Thanks

Mark

 

[cdbe]

Either 4x2 or 3x2, depending on spacing - (but if you went for closely spaced 3x2 you could get away with thinner decking). Same size for wall plate, can be fixed to wall with screws and plugs and joists sat on top. If you have spare cash you can use hangers, chemical anchors etc. Insulation added later would be better in large sheets, held up with battens. Plan your timber lengths - If it's around 1.5m you might get 2 out of a standard 3m length. You'll need to give the rainwater drainage some thought.

 

[Marker121]

Thanks good point about drainage.

I've Just re-measured and its only 3.2m long so maybe i can do this:

Go down the joist hanger route and then running noggins down the center between each and then use thick long firring pieces down the 3 long lengths to fasten my OSB to? would this work its only narrow so should be strong enough?.

Ventilation I was thinking just leaving the end of the firring pieces slightly thicker then there will be a channel down each and more strength towards the thinner end?

Thanks for you help

 

[23vc]

Or do away with the firrings and fit the wall plates with a fall.
cross ventilation above any insulation could be done by notching the top of all the short rafters I guess. Probably only really becomes relevant if the whole things supposed to be warm and air tight