Insulating Old Cottage Roof - Advice Needed

Bluscreendream

Hi Guys,

I need a bit of advice here. Im currently renovating an old cottage on a very tight budget and need advice on insulating the roof. The cottage is a bungalow with no ceiling (see attached pic) and the rafters run up into the apex. The external roofing is corrugated metal sheeting. I have already purchased rolls of 100mm knauf Loft Insulation (see attached pic) which I plan to put in between the rafters and then cover all of this in with double-sided Alububble (see attached pic) and then cover everything in with plaster boards. I've been advised by a 'friend of a friend' in the trade that these two layers of insulation should be sufficient but Im a little bit worried.... could anyone be kind enough to give some advice on weather these two layers of insulation would be enough to insulate a metal corrugated roof on an old cottage as Im starting to have my doubts. Any info is much appreciated.

Thanks!

Carlow52

what is behind the polystyrene between the rafters?

IMO u need to consider ventilation in this roof space.

In addition I would not be happy to leave the poly styrene exposed: fire risk.

Could be wrong

Bluscreendream

Hi Carlow52,

Thanks for your post. Please ignore the polystyrene sheets in the photo, these will be removed. The black stuff is a felt type membrane.

Thanks.

Carlow52

Thanks for reply.
The ventilation issue still arises.
U cant just shove 100mm of insulation up against the felt between the rafters. and then cover it with the alububble

You will have a condensation problem which may rot the rafters.

U need a 50 mm ventilation gap between the felt and the insulation which will then be vented at the ridge.

If I were u I would put in high level collars as the one shown against the chimney breast and go across flat at this point, with 12-16" of glass fibre insulation on top.
You can then vent the top roof space


I know I am not answering the question you asked yet because I want to get the detailing right first.

There are others more skilled than I here who will answer the question

Bluscreendream

Hi Carlow52,

Thanks again for the info, it never actually occurred to me about the required ventilation gap :rolleyes: but I will definitely incorporate this when I start insulating.

Thanks again.

Carlow52

Bluscreendream wrote: »

Hi Carlow52,

Thanks again for the info, it never actually occurred to me about the required ventilation gap :rolleyes: but I will definitely incorporate this when I start insulating.

Thanks again.

Glad to point you in the right direction:).

Have u ventilated eaves?

There needs to be a flow through, normally up, over and down

The tin roof means that replacing the felt with a breathable membrane is not an option, so venting needs to be in the gable end, hence my suggestion on the high lever collar

Anyway look on line for the detailing
most sites selling insulation will carry the details

or buy the homebond book: 50 euro, great value, much cheaper than the fees here:D

Bluscreendream

Carlow52,

Thanks again, my father actually has that book so I'll rob it off him the roof on the cottage is basic stuff so I'll have to have a good read of that book and try to figure out how I can create an air flow. Thanks again

Bluscreendream

So regarding my original post on my insulation plan for a metal corrugated roof.... would anyone have opinions on if it would be sufficient? :rolleyes:

Thanks

johney

can I ask Carlow what you mean by

"The tin roof means that replacing the felt with a breathable membrane is not an option"

Stoner

Bluscreendream wrote:

So regarding my original post on my insulation plan for a metal corrugated roof.... would anyone have opinions on if it would be sufficient?

Would you not have it sprayed with breathable insulation ?

Finished very well

Would you not try 35 or 50mm Thermo board on top of that then? Skip just the regular plasterboard