Need a shallow warm deck flat roof...

[machineage]

Hi all!

I am extending my integral garage & having a change of use for a part of the existing garage. The extended garage & change of use spaces will be under a single flat roof.

However - I am restricted with the flat roof height due to an adjoining pitched roof which runs onto it. I have to increase the floor height for the change of use space by 150mm to form the required step into the garage space - and to level it with the existing habitable space into which it will flow. The new roof will be a warm deck with 100mm+ insulation.

All of this means I am now incredibly tight on head height for the newly formed habitable space - and will be down to around 210cm using traditional timber roof beams. Is there anything people could suggest - or are there shallower members available for supporting a flat roof? The spans are 4.8 metres and 5.7 metres.

Thanks!

 

[noseall]

I am restricted with the roof height due to an adjoining pitched roof which runs onto it.

What does this mean exactly?

 

[machineage]

Sorry noseall - I meant where the flat roof meets the eaves of the existing pitched roof. There is also the added complication of a box gutter from the side elevation of the pitched roof which runs onto the flat roof at the highest point in a corner. Maybe some photo's of this would explain better

 

[Xenon]

You can create a gutter in the insulation by using a thinner insulation. We usually do this when window cills are an issue.

 

[hardmetalking]

Xenon - doesnt this create a cold spot in the roof?

Have you thought about a warm zinc roof? All the insulation can go on top of the rafters which helps with head room.

 

[Xenon]

Xenon - doesnt this create a cold spot in the roof?

Nope, a 50mm insulation board 300mm wide will be fine for a gutter.

 

[tony1851]

What size (depth) timbers are you using for the roof structure? If you've taken them from the published load/span tables, they are a bit conservative. It's possible to use shallower joists in certain circumstances, eg by spacing them closer together.

 

[hardmetalking]

Zinc is also a lightweight option as its only 5kg per square metre.