Garage roof construction

[alexhayes]

Seems like i`m making progress with planning the garage. Last bit of the jigsaw is the roof.

Garage plan dims, 4m wide x 8m in length.
Garage door on front 4m face, 3m wide opening and 1.98m high
1.5 brick piers adjacent the opening
another set of piers mid way along the 8m length walls

eaves height of 2.2m (this is required for up and over garage door)
ridge height cannot exceed 2.5m for planning.

i`ve binned the idea of gable ends in brick. I`ll upvc panel the front and rear walls between the eaves and roof. Up and over door can attach to piers/goalpost and removes need for lintel above door opening which was causing issue with ridge height.

I was thinking of premade truss's for the roof, is that a bit overkill for a garage? or could i not just form a bolted traingle from some pretty substantial timbers, space those at every 2m and ply board between them? that spacing seems a bit high if i`m going to be asking someone to lay felt on there, maybe 1m truss spacing? and do i need a member running down the ridge?

as you can see i need some help. According to my degree this should be well within my capability, but i`ll be dammed if i can find any of my notes on timber design.

any pointers- bar ring up a flat roof specialist and let him bum rape me.

 

[Shytalkz]

Is that a 300mm rise you mean, or +2.5m from eaves height?

 

[alexhayes]

a poxy 300mm rise.... so a 4m wide truss with rise of 300mm, meaning i can't tile the roof if i wanted to.

Unless i want to go down the planning permission route, which i`ve been told they will probably refuse anyway.

Cheers, apologies if that was not clear.

 

[Chukka63]

flat roof????

 

[noseall]

Your height constraints are limiting you to a flat roof and you should build it as such.

Anything else will look weird, be a pain to build and be just...er...wrong.

Maximum rafter/joist spacings of any roof i have ever built is 600mm.

 

[alexhayes]

Looks like flat roof construction then, strange how you railroad yourself into an idea.

Ok then, so i have an door frame height of 2.2m at the front face, and a max build height of 2.5m at the front face. This means i can put a lintel/catnic back in over the door opening and brickwork up to the 2.5m height.

Questions- 8m length of flat roof, what fall should i go for. I dont fancy having 5` of headroom at the back of the garage.

Brickwork, on the side walls should this fall with the gradient of the roof, thus giving me somthing to attach roof joists to, will that be ok on a single skin?

Joist size for spanning 4m, and spacing.

Joists in timber or steel?

cheers people i am trying to get this right, if i do indeed get a decent garage up without major trouble i`ll owe it all to you lot.

 

[alexhayes]

Ah, google is king.

and i now understand what a wall plate is...

http://www.delston.co.uk/joists.htm

50x 195 at 600 c/c? that should sort my clear span, with noggins in the centre of span.

So looking at this diagram

do I build all the walls up to 2.2m (the required clear height for door frame), then use the 195 depth timbers to form the lintel as such over the door opening, and then at 600 centres along the roof. I can then facia the timbers.

This means the roof is flat, proper flat, no fall- is this correct? i`d imagined i needed some fall, and this is where i was struggling to see how i`d build a sloping roof structure if my walls are all flat.

Are flat roofs actually dead flat?

EDIT:

If i had read it all before posting i`d have seen this:

A firing should be fitted to each joist. Firings are lengths of timber cut down the length from corner to corner forming very long triangles so that they go from full thickness to nothing and lifting the one side of the roof creating a fall. This fall being directly proportional to the thickness of the firing in relation to its length. Firings can be obtained at all good timber merchants. It is usually easiest to put your insulation in at this stage if the cold roof system is being used.

 

[noseall]

Direction of fall will depend upon gutter overhang location. If you are building close to your boundary then overhanging your gutter on the long side may be a no-no.

If you have the room though, then it will be sensible to fix the gutter on the long side.

Don't forget to extend the plywood sheets 50mm or so, beyond the fascia line to form a drip into the gutter.

Firring strips are also known as diminishing strips.

200mm x 50mm deep joists should be fine for a 4m span, but i would fix them at 400c/c.

You will only need a lintel over the garage door if you intend showing any brickwork above the door. For all intents and purposes you could actually build without it or make good with timber cradling and fascia/soffit or pvc cladding etc.

 

[alexhayes]

Don't forget to extend the plywood sheets 50mm or so, beyond the fascia line to form a drip into the gutter.

200mm x 50mm deep joists should be fine for a 4m span, but i would fix them at 400c/c.

Cheers, i would have missed the 50mm. I will put the guttering on the long sides, i'll also start building 200mm away from the boundary hedge, which should give me enough space. i`ll have a word with neighbours first though , it will sit over a hedge thats about 0.5m thick, so i should not be over my boundary.

why the 400 c/c? is board better available in that width and less cutting? Saying that i dont fancy a roof and snow falling in on what i will eventually put in there. i`d cry.

400 centres and sleep easy when it snows i suppose- plus nice and easy to insulate.

Yep i`ll probably use one of the joists at the front face above the 2.2m brickwork. I can fix the 3" goalpost for the door to it, and then use upvc etc as a facia to the undersidse of the baords.

This is a lot more work then i`d thought it would be. I can see my spring/ summer being eaten up.

Thanks so much for help!

Alex

 

[noseall]

why the 400 c/c? is board better available in that width and less cutting? Saying that i dont fancy a roof and snow falling in on what i will eventually put in there. i`d cry.

400 centres and sleep easy when it snows i suppose- plus nice and easy to insulate.

2.4m x 1.2m plywood sheets will work with either 600mm or 400mm centres. Just make sure you are using European fellas as the Yankee stuff is still in old money and you will end up trimming them to fit.

I personally don't like 600mm centres, and i would be inclined to fix them at 400 anyhow. You will also need to fix solid bracing or bridging at mid-span as indicated (noggin) in your diagram