Insulating flat roof?

jdpl28

Hi all,

I have a flat roof with no insulation in it at all. It's above a bathroom, so I'm getting really bad mold build up on the ceiling, not to mention the bathroom is always freezing. How would I go about insulating it? Could I insulate it from above? rip down the ceiling and add it from there? Or blow in insulation? And do I have to leave a gap at the top of insulation for ventalation? What complicates it slightly is I've got spots in the ceiling, and you can't have insulation near spots?

thanks,
J

muffler

Can you replace the flat roof with a pitched roof?

jdpl28

Not really. Plan is to do that eventually, but that's big money. It would be part of a bigger extension.

smashey

What size is it?

ardara1

YOu've 2 choices if you're going to insulate the roof as it sits.
If you insulate between the joists (and below also to do the job right) you MUST introduce ventilation on the underside of the plywood decking 50mm - getting air in one site of the joists and out the other. Otherwise there will be condensation build-up under the ply.

The other option is to create a WARM ROOF and insulate over the flat roof.
If the waterproof covering is in good nick you can place EXTRUDED EPS over the felt to create an INVERTED flat roof (Google it) and put a separating layer over the insulation then stones.

If the covering needs replaced you could put 120mm of Kingspan/Xtratherm over the decking - then ply - then felt. BUT be carefull with the edge detail - there'll be no insulation at teh wall/roof junction - needs covered.

With all flat roofs, a good vapour control layer to the underside is essential.

jdpl28

thanks for that. The roof is about 3m squared. I'll look up the warm roof now. Was also thinking of a green roof? Anybody any experience with it?

John Mason

i was in the same situation myself and i ripped down the ceiling and insulted myself, just pinned the insultation stuff to the ceiling beams. funny enough, it made no difference whatsoever, the bathroom was still freezing, but my flat roof started to leaking the january storms and i replaced the whole roof, the difference is unbelievable, it is so much warmer:)

Mellor

the easyiest way to do it is the way ardara detailed. whats the roof buildup?
ans whats the junction between roof and wall like (two story wall not eaves)

galwaytt

Dow Roofmate insulation, an XPS, is good for this application. You can get it from Insulation Distributors in Dublin (no connection, btw, except that I use a similar Dow product for a not-dissimilar application.)