Insulating my home including roof, flat roof and other areas
Information, help, tips and advice on cavity walls, ceilings and lofts etc....

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Joined: Wed Dec 07, 2022 9:33 pm

Insulating my home including roof, flat roof and other areas

by 31K » Wed Dec 07, 2022 10:27 pm

Hi all, this is my first post and I hope it's in the relevant section. If not please let me know where it should be and I'll repost in the correct place.

I'm hoping to get some advice on insulating my home which in many places feels like a shed. The other day after returning from a few days away (heating was turned off, maybe I should have left it on low instead) the bedroom was 7 degrees! So, I think I better insulate the areas I can considering the cost of living crisis and need some opinions. I will try to break it down into the sections as I plan to insulate them.

1) Pitched roof at the top of the house

This area is approx 7m X 3m and not tall enough to stand upright in (I have to crouch a little). I am planning on creating a cold roof. I am looking to use the following as an initial layer: ... oll---8-3m²/p/166877

I am looking to then lay the following at 90 degrees (on top of the initial layer) so that there's a total of 300mm of insulation: ... ll---5-61m²/p/109451

I would like to board approx half of the loft space and will use 210mm loft stilts/legs (roof joists are 120mm) to allow for the 300mm of insulation underneath. I know this should not be compressed, however will there need to be an air gap between the insulation and the bottom of the boards?

Considering the loft space is already limited, is there a better alternative?

By better I mean, something that has lower profile with a similar u value (I think this is the correct term) maybe PIR board like Celotex or Kingspan, possibly removing the need for loft stilts/legs. This will both save money (which can be put towards the potentially more expensive insulation) and space.

2) Flat roof at the front and back of the house (same level as the pitched roof in the point above)

This currently has no insulation and is above the upstairs bedrooms/bathrooms.

The area is approx 7m X 2.5m at the front and the same at the back. I am planning to create a cold deck of insulation. I have a little over 120mm (height of joist) of space between the bedroom/bathroom plasterboard ceilings and the ply (assumed). This will be done without removing the internal ceiling or the flat roof externally as I have found a way to access the flat roof from inside the pitched roof (lucky I know, at least I hope anyway until someone tells me otherwise).

I am looking to use the following as it will give me some flexibility (when working around a water pipe feeding a overhead shower) and I will use a telescopic rod or poles to push it down towards the eaves (I know these should be kept clear, I have measured to the end and will set the rod/pole to a slightly shorter length) I have also selected 50mm insulation as this will give me more than the minimum 50mm of ventilation gap needed between the insulation and the ply. Is this correct and could I push this to 75mm instead? ... RcEALw_wcB

Some of the rooms have spotlights, I was looking to pull these out, push the insulation in and cut it away from inside the room before re inserting the spotlights, will this be ok?

Also I believe there is a vapour barrier on the plasterboard which looks like some type of foil, is there any way to confirm this?

It is worth knowing that I can only see the end of the eaves on every other void in the flat roof as every other void features a noggin between the joist (I will insulate up to the noggin in this case as some insulation is better than nothing).

3) The walls upstairs are timber frame with a half height pitched roof externally (flashing is just below the window) and hanging vertical tiles either side of the windows. I will be looking to cut a hole inside the room big enough to crawl through (only need to cut one hole at the front and one at the back as the voids go all the way across) to create a cold roof in this space. Will the Knauf 100mm and 200mm insulation be suitable for this? I will then use PIR board on the walls up to where the half height pitched roof meets the wall. I hope that makes sense.

I am then looking to remove the external hanging vertical tiles, install the PIR board on the areas I am not able to reach from inside the half height pitched roof voids and install cladding.

Appreciate this is quite a large post, but any advice would be appreciated.

I will add a picture of a diagram to help visualise things and post pictures where I can.

Thanks in advance!

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