New roof design


I’m building a lean to garage 15ft wide 30 ft long 5 dgree pitch (virtually flat)and was going to use 2x9 timber on 2ft centres with 1/2" ply covering and torch felt to finish. I’ll put some 2x1 lath across the beams to better support the ply joints and some silver bubble type insulation under the lath. There is no code to work to and very little chance of snow.
Does this roof sound OK ?


Codes vary by where you are located. Here 24" oc requires 5/8" by. May be different in your area. You need to check local codes. 15x30 = 16 sheets so check your local codes, an extra 3 or 5$ a sheet , 100$ can make the difference bewtween the structure passing inspection or being forced to re do everything.


How long is the span is the big question, 2x10 should only span 10’ or so on a low pitch roof.
You can get span tables on the internet


Sounds awesome!!
Your roof will be perfect too because of your width you can achieve no side seams.
And use all of your material up with almost zero waste.
Overhang the torch material 5/8s or so
Past the metal edging
So when it shrinks in the future
It will shrink to the edge of the metal
Instead of shrinking back from it.


Span is 15ft and I was thinking of using 3/4 ply, the 5/8 isn’t so common around here
I did another very similar roof spanning 16.5ft a few years ago using only 2x8 but with steel sheet roof and permeable membrane underneath-no sagging so far but too cold in winter and too hot in summer The materials on this new roof weigh a lot more than thin steel roofing sheet.


I would want to use at least 2x12,maybe even 14" Tji’s. Last thing you want is a saggy roof that can’t be fixed easily.


I found a span chart here
For flat roof joists It says 50x225 (2x9) for a 4.47m (15ft) span allowing for a 2ft snow loading.
We never get 2ft snow ! maybe 4inch max once a year
I’m in UK BTW


Ahh, very different world then. That would not hold up here


Ya sounds like awesome .


Eventually got hold of building control and they are OK with the 9x2 timber on 2 ft centres.It’s an outbuilding/garage so not too bad if it develps a little sag after a few years I doubt it will collapse !