Internal or external wall insulation?

[thomp1983]

Hi all.

I live in a chalet bungalow, downstairs is a standard brick/block with cavity arrangement. Upstairs both bedrooms are single block work with no cavity.

The bedrooms face north and south and the north facing room is a good 3 to 4 degrees colder than the south facing room, this temperature differential makes all of upstairs cold.

Externally both bedrooms have upvc cladding fitted, am I better removing the cladding and fitting external wall insulation to the north facing room then refitting the cladding or fitting 100cm celotex internally to the wall?

My concern with insulating internally is the wall has the radiator hung on it so I'd need to install some sort of mounting for the radiator, also I'd be left with a really deep window which I think would look odd.

Which method would you go for?

Kind regards,
Chris.

 

[noseall]

Insulating internally means the results will be more immediate regards heating/cooling returns, i.e. no thermal mass to worry about. The disadvantages are the fact that you introduce a weak fixing surface to the wall. Usually only a major issue when fitting kitchens etc.

100mm internally to an existing cavity wall seems like a lot...? But fair play if you can spare the space.

 

[thomp1983]

100mm was just a nominal figure. How about 50mm celotex direct to the block wall then a 3x2 cls stud wall built in front of the celotex with the small side out in filled with 25mm celotex (this would leave a 13mm gap in the frame work), I can then build extra studs into the wall for hanging the radiator on and finish with plasterboard.

Would 75mm of celotex provide a noticeable difference?

Thanks
Chris

 

[noseall]

Would 75mm of celotex provide a noticeable difference?

To a cavity wall? Yes. But you'd have to make sure that you improve or address all the cold spot areas (roof/ceiling etc) and look at the quality of the widow fit, flooring gaps and general air-tightness, too.

 

[thomp1983]

It's not a cavity wall, it's a single skin block wall

 

[Ivor Windybottom]

If at all possible, it would be better to move the radiator to one of the internal walls that you won't be insulating anyway. Insulated or not, radiators on external walls waste lots of heat by pumping it straight out through the wall and/or window. But often it's the only practical place in many bedrooms due to all the furniture elsewhere.

I'd prefer internal insulation normally. But in your case you have cladding outside already so perhaps it would make more sense outside - you wouldn't be covering cotswold stone or anything. Plus of course then your room wouldn't shrink.

 

[^woody^]

Do you want 120mm smaller rooms and the disruption, more technical design detailing and issues with services? That's the main consideration.

If you have room for external insulation, that's almost always preferable. But there are some detailing considerations to avoid thermal bridging and potential internal cool spots - reveals, roof abutments and flashing, type of cladding.

 

[thomp1983]

The disruption isn't such an issue, the whole floor is getting taken up in the room in question to fix some previous bodges the house has suffered so I'll have access to everything that needs altering.

The room is a spare so the general loss of 120mm shouldn't make much of a difference

 

[StephenStephen]

EWI keeps the thermal mass on the inside, which will slow down temperature changes - it'll heat up more slowly, and cool down more slowly.

 

[Ivor Windybottom]

Just ensure the walls are dry. Otherwise you'll be trapping all the damp inside airtight insulation, instead of it evaporating off to the outside air.

This is normally only a problem with a ground floor though - rising damp coming up from the ground.