# Garage roof costs



## fandango1 (26 Jan 2010)

Got a quote to build a garage 8m x 8m.

Quote includes using an insulated steel roof (flat roof) - apparently like you'd see on factories. Mrs Fandango1 & myself would prefer a pitched roof and are waiting on an updated quote. 

Just wondering if anyone out there would estimate what the cost difference between the two roof types would be.


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## onq (26 Jan 2010)

A pitched roof could go quite high depending on the pitch.

8M front to rear would mean it'd be like a house roof.

I'm assuming you have permission for the garage.

64 sqm is way over the 25sqm exempted area.

Its 4 mid-range saloons and two hatchbacks.

Assuming it has a clear span structure.

And they can park in sequence 

ONQ.

[broken link removed]


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## fandango1 (27 Jan 2010)

Yep, have permission and space to build a big one. Will have a wood pellet boiler and large pellet store in one section which will use about 9-10 sqm. Want enough room for lawnmowers, motorbike, bicycles, car and a work area, so am happy enough with the size. Main concern now is the cost of the roof.

Can understand a flat roof means using fewer blocks as there are no gable walls as such, and the area to be covered is also smaller than a pitched or hipped roof (hipped won't work because the building is square), but just trying to get an idea of the cost differences.

Flat roof:
T-bar steel supports & PU insulated sheeting for roof

Pitched roof:
Timber trusses and either tiles or PU insulated sheeting (maybe something like steel sheeting that looks like tiles - see www.skyclad.ie , no affiliation)

So real question, what would be cheaper: steel t-bar supports for a flat roof or extra block work and timber trusses for a pitched roof.

Is there a minimum angle for a pitch roof?


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## onq (27 Jan 2010)

The minimum angle depends on the covering material, fixing method and the backup membrane.
There is no problem doing a hipped roof on a square building, its just the top sheets get a tapered cut
Most houses are "square" so I'm not certain where this arose - are you thinking of the detail at the meeting point?

If you want a pitched roof with no cuts in the sheeting material consider a monopitch.
A double-monopitch is next up, and I think this may be what you're thinking of.
Low pitch monopitches may have a problem if they're not securely fixed.
The roof covering/ structure can blow off, as it can flat with roofs.
Double-pitch or hipped roofs tend ot be more secure in this regard.
The detailing of the foor, its covering, insulation, support structure all bear on the cost.
Unless you submit a fully detailed design for costing to a QS or go out for costing to a contractor, you won't get a useful or reliable answer.

ONQ.


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## fandango1 (27 Jan 2010)

Thanks for that. Think it is a double pitch that I'm thinking of - bit like an A shaped roof. Am open to various finishes so will see what new figures the builder comes back with for changing the roof.
Based on your descriptions, builder had originally cost for a monopitch rather than a flat roof. Think there was about a 10-12 inch drop front to back.

Thanks again


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## onq (27 Jan 2010)

You're very welcome fandango1.

That's circa 300mm over 8600mm allowing for walls or around 2 degrees, well under the 10 degree slope that most people understand to be a flat roof.

Its even well below the 3 degrees that might be a minimum for Kingspan metal decking. 

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I'd be wary of going so low.

You could consider a membrane system, but my experience is that unless they are covered with a protective covering they can perforate and/or ponding can occur.

FWIW

ONQ

[broken link removed]


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