Help me calculate floor space in my loft

jas72 · 18 Oct 2009 at 16:09

I'm thinking of getting my loft converted and have to raise the pitch of my roof from 30° to 40°

MY house is detached and is 8m X 15m of useable loft space but of course I won't have it all. I was looking for a calulation as I'm sure it's quite simple to do but I can't work it out

jas72 · 18 Oct 2009 at 16:30

Well the height in the center of the roof will change if I change the (pitch) angle of the roof, legal floorspace is calculated at 2.3m in height so whilst technically i'll have 8X15m floor space i'd like to know what floor space i'd have where the height will be 2.3m or more.

I've found a site that shows with a 40% pitch my height at center will be 3.35m

now to calculate how much headspace that gives either side.

jas72 · 18 Oct 2009 at 16:38

Orcish-Horde said:
Correct me if am wrong.... You are converting you roof space but have to replace the whole roof and you don't know how much usable space you are going to end up with or have to start with? If you are having the roof removed why not just keep the old roof and build the brick work up 4 foot and then put the roof back on.

It's a possiblity as well of course but the roof is now 30 years old and it's trussed I probably couldn't keep it without loosing my ceilings below.

But yeah there are some minimums for lofts The steeper the pitch the headroom I get.

jas72 · 18 Oct 2009 at 16:40

Abyss said:
At 2.3m minimum headheight you will lose 2.7m either end off the 18m.

It's easier to think in terms of what space you lose in the corners. Using a website like http://ostermiller.org/calc/triangle.html put in the 40 degree angle, 90 dgree angle and vertical height required, and it will tell you how much you lose each end.

thanks but the roof sits the other way and is 8m wide.

jas72 · 18 Oct 2009 at 21:20

thanks for the replies guys.

I've tried working it out using calculator tools and I clearly would benefit from raising the pitch of my roof.

I'm looking to add 2 large bedrooms and a bathroom upstairs.

Great idea about the 1.2 as useable

If I take the right angled triangle and use

30° as my pitch my height at center is 2.3m this gives me around about 2m wide at 1.7m height which is clearly useless in terms of having a liveable space.

However by changing the pitch to 40°then the height at center is 3.36m which gives me around about 4m at 1.7m height and 5.2m at 1.2m giving me 15X5.2m useable floorspace