Cold room above garage

[Adamed13]

After some advice please (see picture also)

I have an integral garage with a bedroom above. The roof of the house is kind of split level (not sure of the professional name for it) and the bedroom has a dormer window.

The bedroom (my daughters) is so cold overnight and when the heating is off (gets down to 10 degrees often) and the 4th bedroom (used as an office) is similarly cold at the back of the house.

Above the garage door is a vented soffit. I was wondering (or if this would be a bit far fetched) if the cold air would be gusting through the ceiling/floor void and making both rooms cold? The floors of both rooms are noticeable cold under foot.

I am looking into having the garage ceiling over boarded with insulated plasterboard and having the bedroom above redecorated but wanted to sort out the cold first.

Any advice welcome.

 

[JohnD]

@Adamed13

I'd lift the bedroom floor and pack mineral wool (loft insulation) tightly between the joists.

It is common for cold draughts to blow around these voids, and come up under the skirtings, and between floorboards. Pack very fully around the edges of the room where draughts come up.

I only use the wool treated with Ecose (it is brown) which does not shed irritant dust and fibres. Made by Knauf but widely sold as an own-brand in DIY chains. "Ecose" will be marked on the wrapping. Example: https://www.wickes.co.uk/Knauf-170mm-Standard-Top-Up-Loft-Roll-Insulation---6-47m2/p/109450#
Your joists are probably about 170mm high. You can cut it with a breadknife or fine-toothed saw. Big wallpapering shears can cut it but are slow.

Easy to do becuse you can push it into irregular gaps, unlike rigid foam which has to fit perfectly.

Mineral wool is non-flammable, which I think can be a great advantage.

If you find cracks or gaps around joists or edges of the ceiling below, seal them with expanding foam (I use the pink, fire resisting grade) after vacuuming away dust and dirt and spraying with water. There may be gaps around pipes or cables.

Put the insulation underneath waterpipes to protect them from cold.

if the old floor is chipboard, consider throwing it away and putting down ply instead. Put struts (noggins) under all unsupported joins.

 

[^woody^]

As above, but I'd put at least 50mm Celotex directly below the floorboards, and the rest in quilt.

It's important to fill around any joist bearings in the wall with flexible mastic, and fill any other gaps in the wall in the floor void, to stop any draughts and air leakage. Similar mastic (intumescent) around the garage ceiling and holes such as the light fitting.

 

[diy_fun_uk]

Looks like quite a new house, good to see the builders have excelled themselves with semi-decent insulation ...

 

[23vc]

Yep, when I did one as part of an extension years ago, building control wanted loft roll type insulation between all joists and 50mm underneath (and fireline plasterboard) which lines up with JD and woody’s points above.