Extending into attic - roof height and projection level?

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pudzer

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Hi! Am thinking of extending into attic. The height at the apex of the roof is 2.4m high which is fine. However, how do I work out how much habitable space I will get if angle of the roof is 38 degrees and width of the roof is 10.6m (it's a gable end roof). There must be some formula somewhere?:confused:

I suppose I need to find out what height you can go to in the roof to consider it habitable or are there regulations?

Thanks for your help.
 
The convention we use in our office designing dormers is to be found in TGD F Ventilation...
This states that for a room to be considered 'habitable', the ceiling height at 2.4m must be greater than half of what it would be at 1.5m...

Height of Habitable Rooms​

1.13
Ceiling height is one of a number of factors
which affect ventilation of habitable rooms. The
suggested dimensions in Diagram 5 are consistent
with good room design, the use of standard materials​
and good building practice.

you can find it here, on page 10 of 15, with a diagram..
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1647,en.pdf

the wording here is a bit ambiguous, but we hold it as being the regulation....

In order to work out what floor space we would need to know the length of the attic, ie from gable to gable....

I just did a quick diagram and you should have no problem with attaining habitable space up there... assuming stud walls at 1.2 m that would give you 7.5 m wide floor space... so just mulptiply this by the lenght of the attic and you will have your floor area...... (its a fine sized attic, may i say)...
h

​
 
Hi SydtheBeat

Thank you for your very informative reply!

I read through the document that you provided and looked at the diagram. Is it correct to assume that 2.4m is the minimum height for a ceiling in the attic and that 1.5m is the accepted norm for the walls or can it be at 1.2m as you suggest in your e-mail?

By the way, the length from gable to gable is 20.865m so, it would give me an extra 156sq m if my calculations are correct. Mmmmm, that's a nice size for a snooker table but who'd carry that up two flights of stairs?!!:D

Thanks again for your help.
 
yeah, 156 sq m is 1680 sq ft... thats huge!!

the stud walls are usually at 1.2 m but there is not fixed regulation as to what they have to be at.... it all comes down to retaining the structural stability of the attic....

are you going from a cut roof to a dormer, or from a truss roof to a dormer???? i hope you have an architect / engineer engaged to inspect the work....

remember you also have to comply with fire regs if you are going to have bedrooms up there... (actually whatever you are going to use the rooms for, i would advise having the comply with escape regulations)...
 
Hi again,

Yes, I have an architect though I tend to do 90% of the work! To be honest I don't mind as I know what I want (do you reckon I'm female?:D ), I usually research what I want versus what I can have and then run it by my architect - it saves him time and I like to know what's happening.

Unfortunately, we can't cut out a dormer roof - well, not to the front anyway. We did apply for it in our planning application on our new build but it got turned down. However, they did say that they "may allow skylight windows to the rear of the dwelling". My understanding was that you could you do almost anything with windows to the rear of your dwelling??? I will also discuss the possibility of adding dormer windows to the back - can I do that without planning?

Thanks!
 
To be black and white with your question.. NO is the answer.....

anyway, the attic conversion itself requires planning permission (assuming you were given permssion for a single storey dwelling in the first place).... so include the dormer windows to the rear as part of the application..
 
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