Insulating an old 1930’s top floor flat roof apartment

craig88b

After the recent green grant I’ve been thinking about what I can do to my 2 bedroom apartment to get it to be warmer. It is a top floor apartment with a flat roof so realistically I can’t do any insulation to either the roof or the cavity walls externally. It does get pretty cold in winter and I am intending to up date the old damaged double glazing windows. But other than that not sure what is “easy” to do that will make it much better. There is currently no radiator in the bathroom, only an electric towel heater than I usually leave off. The living room struggles to get above 20 degrees on a cold night even when turning the gas radiator on full for a few hours. The epc is apparently an E(44) and has the potential for C(69) with “flat roof or sloping ceiling insulation” which is very generic. I have a smart thermostat. 

Other options would be upgrading the boiler as the potterton suprima 30 I currently have I don’t think is condensing but that’s also a lot of money for a small efficiency. Also considering replacing the front door with a composite one. 

MovingForwards

How high is your ceiling? Potential insulation in that and the floor or a false ceiling and insulate that.

Are the radiators sufficient size in each room to heat it, or would having larger ones be better?

What's the square footage of your flat?

Do you get much sun into your home? If not then it's not warming up naturally and you are having to start from scratch each time.

@FreeBear and @Doozergirl are probably well placed to give better ideas.

Doozergirl

What condition is the roof in?  Could it do with replacing?  The current method of re-roofing a flat roof is to put uninterrupted solid insulation over the joists as part of the reroofing.

Makes sense to do it as part of something that is going to last decades and do the job correctly.  
 

craig88b

MovingForwards said:

How high is your ceiling? Potential insulation in that and the floor or a false ceiling and insulate that.

Are the radiators sufficient size in each room to heat it, or would having larger ones be better?

What's the square footage of your flat?

Do you get much sun into your home? If not then it's not warming up naturally and you are having to start from scratch each time.

@FreeBear and @Doozergirl are probably well placed to give better ideas.

Thanks for the reply. It’s about 50sqm 2 bed 1 bath flat with “normal” ceiling height. Not at home now to measure but probably about 3m’s? The bedrooms have biggish size
rads but the living room one is a bit smaller
and not as powerful. The living room
and main bedroom are south facing so they get a good amount of sun. The second bedroom, kitchen and bathroom are north facing and have smaller windows so not too much sun. The main bedroom is the warmest as it has cupboards along the whole length of the one internal wall and secondary glazing too. 

craig88b

Doozergirl said:

What condition is the roof in?  Could it do with replacing?  The current method of re-roofing a flat roof is to put uninterrupted solid insulation over the joists as part of the reroofing.

Makes sense to do it as part of something that is going to last decades and do the job correctly.  
 

Thanks for that. To be honest I don’t really have much/any control over the roof as it is an apartment with a freeholder that does that stuff and don’t think they’re too interested in doing a full refit anytime soon. 

I was thinking my only viable option would either be to use something like wallrock kv600 on the internal(external)walls and ceiling or glue/bolt kingspan type boards to those
walls? 

FreeBear

craig88b said: I was thinking my only viable option would either be to use something like wallrock kv600 on the internal(external)walls and ceiling or glue/bolt kingspan type boards to those walls? 

Don't go wasting your money on the KV600 - It just doesn't have the thickness to provide any worthwhile insulation. If you are going to insulate the walls & ceiling (you may need the leaseholder's permission), you'll need at least 50mm of polyurethane or polystyrene.  Depending on the wall construction, you may get away with 65-75mm insulated plasterboard on the walls and 75-100mm on the ceiling. Detailing around the windows will need careful attention so as to avoid any cold spots...

Ideally, you'd want to take all the plaster down to minimize the loss of space, but lime plaster is messy (but it can be recycled very easily). In terms of cost, it depends on how much of the work you want to do. Materials would be around £1K, and maybe £400 per room for plastering. You'd also need to budget for replacing skirting board, architrave &  picture rails.

Building regulations may kick in depending on how Building Control view the work - Normally, if you remove more than 25% of the plaster on external walls & ceiling, insulation falls within their remit. Whether this 25% rule applies to just your flat or the whole building would be down to interpretation of the rules.. There is also a cop-out clause that says any work should have a pay back of (from memory) 15 years. If the projected savings are less than the cost of the work, then you only need to do the best you can within the budget.

Is it worth insulating a 1930s building - Heck, yes. Did a small box room (1920s, solid brick wall), and noticed a vast improvement as the insulation boards went up. Now that the room is (almost) finished, a tiny little 500W radiator will keep that room nice & toasty.

craig88b

FreeBear said:

craig88b said: I was thinking my only viable option would either be to use something like wallrock kv600 on the internal(external)walls and ceiling or glue/bolt kingspan type boards to those walls? 

Don't go wasting your money on the KV600 - It just doesn't have the thickness to provide any worthwhile insulation. If you are going to insulate the walls & ceiling (you may need the leaseholder's permission), you'll need at least 50mm of polyurethane or polystyrene.  Depending on the wall construction, you may get away with 65-75mm insulated plasterboard on the walls and 75-100mm on the ceiling. Detailing around the windows will need careful attention so as to avoid any cold spots...

Ideally, you'd want to take all the plaster down to minimize the loss of space, but lime plaster is messy (but it can be recycled very easily). In terms of cost, it depends on how much of the work you want to do. Materials would be around £1K, and maybe £400 per room for plastering. You'd also need to budget for replacing skirting board, architrave &  picture rails.

Building regulations may kick in depending on how Building Control view the work - Normally, if you remove more than 25% of the plaster on external walls & ceiling, insulation falls within their remit. Whether this 25% rule applies to just your flat or the whole building would be down to interpretation of the rules.. There is also a cop-out clause that says any work should have a pay back of (from memory) 15 years. If the projected savings are less than the cost of the work, then you only need to do the best you can within the budget.

Is it worth insulating a 1930s building - Heck, yes. Did a small box room (1920s, solid brick wall), and noticed a vast improvement as the insulation boards went up. Now that the room is (almost) finished, a tiny little 500W radiator will keep that room nice & toasty.

Thanks for the comprehensive reply.  I was thinking that maybe the wallrock would be a lot of time for minimal benefit. I probably don’t want to go down the route of removing the existing plaster now as that would be a lot more intense and messy than I’d want. 

Would it be possible to just glue the insulated plaster board to the wall and then plaster over that followed by paint? 

Doozergirl

In a word? No. 

Otherwise we'd all do it that way.  You're relying on the key between the current paint and plaster, then the current plaster and whatever that's attached to, to hold up a massive weight.   There's no point in making use of a grant if you're still going to bodge it.  

FreeBear

Going to take a slightly different tact to Doozergirl here....

IF the plaster is in good condition and well adhered to the wall, it may be possible to stick insulated plasterboard up as long as mechanical fixings are also used (they should be used even if the walls are taken back to bare brick). But in a 1930s build, I would expect the plaster to have blown in places, and any areas that have been damp for prolonged periods, suspect. Taking the plaster off the walls will gain you another 20-30mm of space which can be filled with insulation. Taking the plaster off both walls and ceiling gives you the opportunity to add extra insulation between the ceiling joists and avoid any cold spots along the ceiling/wall junction.

The additional cost of removing the plaster will be small in comparison to the total cost - Messy for sure, but worth it in the long run.