Insulating Bathroom

[Don8]

Having our bathroom redone soon and want to insulate the room as it was freezing last winter. It's a standard two bed Victorian terrace with the bathroom on top of the kitchen at the back of the house. It measures, 2.7x3.1m. The two exterior walls are 9" brick. In his quote the builder has offered to either batten out and insulate between or go straight on with insulating board. He mentioned if we go straight on with the insulation you can get cold spots on the walls, but since we are fully tiling this wouldn't be a problem. Is there any consensus on the preferred method? What sort of board thickness should I ask for?

Futher to this we are getting electric underfloor heating. It seems insulating boarding is highly recommended. However the builder has said we he can insulate between the joists instead. We are raising the floor roughly 15cm and then he has said he will marine ply over. Should I asking to fit insulating boards on top of the ply or will between the joists do the job?

Thanks

 

[Ian H]

15mm or 15cm? If it’s really 15cm i’d have a 120mm insulation ontop of the joists.

 

[^woody^]

There is no real advatage in insulating a floor over a heated space. But for U/F heating, just follow the manufacturer's guide. And be aware that underfloor heating works differently to other heating in that there are long warm up times and it needs to be used differently as a space heater.

For a bathroom, there is no real advantange insualting walls either as the time spent in there minimal and there will be a long payback time. A better option may be a heat recovery extract fan.

Anyway, for the walls, 25mm celotex will be the minimum, 50mm better if space allows. Celotex will be more efficient thant the equivalent polystyrene or insulated plasterboard.

Money would be better spent insulating a ceiling with cheaper quilt if accessible. Otherwise Celotex as above.

 

[Don8]

Thanks for the responses. Current drop is 40cm down to the floorboards into the bathroom so two steps down. We're looking to raise it so it's one step. It's a pitched roof, current height 2.26m up to 2.8m. No access above the ceiling to insulate unfortunately, I know we're planning to raise the floor but reluctant to skim height off the ceiling by insulating it as well. Plus we're intending to a loft conversion with a dormer on top in a couple of years

 

[Hans Pullesh]

There is no real advatage in insulating a floor over a heated space. But for U/F heating, just follow the manufacturer's guide. And be aware that underfloor heating works differently to other heating in that there are long warm up times and it needs to be used differently as a space heater.

For a bathroom, there is no real advantange insualting walls either as the time spent in there minimal and there will be a long payback time. A better option may be a heat recovery extract fan.

Anyway, for the walls, 25mm celotex will be the minimum, 50mm better if space allows. Celotex will be more efficient thant the equivalent polystyrene or insulated plasterboard.

Money would be better spent insulating a ceiling with cheaper quilt if accessible. Otherwise Celotex as above.

Surprised that the bathroom fitter didn't advise this him/herself. If the floors are coming up anyway, I'd suggest fitting a radiator with the correct rating for the size and use of the room (note towel rails are not radiators - they will not always heat a bathroom adequately).

It's a nice gimmick, but practically speaking, under floor heating is a cost which you won't really see the benefit of seen as you'll walk through the bathroom in a couple of seconds, into a cold bath/shower cubicle.

Insulating the walls is an added cost which you really won't benefit from either. As you're tiling the walls, they will always be cold regardless of what is behind them. You're better off getting into the loft and laying (criss-crossing) 3 layers of loft insulation down instead. You will feel the difference in heat.

 

[endecotp]

No access above the ceiling to insulate unfortunately

Make a hatch.

 

[Hans Pullesh]

Make a hatch.

You must have access to the roof somewhere in the house? If you're looking to extend into the roof, you'll need access to it anyway? Otherwise, as endecotp already said, put a hatch in - easy enough job to do and will cost you £30 - £50 for a fully functional loft hatch.

 

[John D v2.0]

Insulating the walls is an added cost which you really won't benefit from either. As you're tiling the walls, they will always be cold regardless of what is behind them

I'm not sure that's true, tiles are indeed very conductive so they would feel cold compared with say carpet if you touch them, but if you insulate behind they would be much warmer in winter and less heat loss. This would in turn reduce mould and air movement and reduce heating cost. Internal insulation would also reduce thermal mass meaning faster heat up time.
This balanced against the cheaper loft insulation which also doesn't reduce the room size and is easier to fit, so i would prioritise lift insulation, but i think saying you wouldn't benefit is incorrect.
You can calculate the cost to benefit ratio for any room if you know the cost of your proposed change and the current buildup.

 

[Don8]

You must have access to the roof somewhere in the house? If you're looking to extend into the roof, you'll need access to it anyway? Otherwise, as endecotp already said, put a hatch in - easy enough job to do and will cost you £30 - £50 for a fully functional loft hatch.

Yeah the previous owners did an informal loft conversion which we have access to but there's no real void above the rear bathroom. Here's a couple of pics. When the time comes for a loft conversion we can do a full L shaped dormer like the neighbours

 

[Hans Pullesh]

I'm not sure that's true, tiles are indeed very conductive so they would feel cold compared with say carpet if you touch them, but if you insulate behind they would be much warmer in winter and less heat loss. This would in turn reduce mould and air movement and reduce heating cost. Internal insulation would also reduce thermal mass meaning faster heat up time.
This balanced against the cheaper loft insulation which also doesn't reduce the room size and is easier to fit, so i would prioritise lift insulation, but i think saying you wouldn't benefit is incorrect.
You can calculate the cost to benefit ratio for any room if you know the cost of your proposed change and the current buildup.

Put it this way, noting that this is a bathroom and you'll only be in there for maybe 25mins at a time max, the under floor heating will take how long to heat the room up? With the insulation in the walls, this will be sped up but how much quicker would it heat up?

Whereas if you had ample loft insulation and an up to spec radiator - which would warm up faster? I'd deffo hedge my bets on the radiator and roof insulation as that's where the majority of the heat is lost - via the ceiling.

Also, tiles are always cold regardless of what's behind them - that's just the make up of them so even though the heat is being kept in the room by the insulation - which it will, the tiles will always still be cold to the touch. It'd be more important to heat the air in the room to make it feel warmer.

I've personally been in this position myself and the best combo I found was a highly rated radiator and lots of loft insulation.

I've just seen the design of the room - being that the ceiling is pretty much in the eves of the roof, loft insulation is probably not going to help!!!!

 

[John D v2.0]

With the insulation in the walls, this will be sped up but how much quicker would it heat up?

I never mentioned anything about under floor heating, i was very comprehensive and specific in my answer

Also, tiles are always cold regardless of what's behind them - that's just the make up of them so even though the heat is being kept in the room by the insulation - which it will, the tiles will always still be cold to the touch

Yes i covered that point

I've personally been in this position myself and the best combo I found was a highly rated radiator and lots of loft insulation.

So you mean you tried all the combinations of insulation and compared the measurements, or you just did what you're suggesting and didn't notice any particular issue? The physics of the situation is fairly well understood, heat in has to be greater than heat out. Thermal mass to be considered. And the dew point and humidity need to be taken into account.
Balance heating, ventilation and insulation and you'll be sorted, although less heating would be cheaper and more insulation would be warmer.

 

[Hans Pullesh]

I never mentioned anything about under floor heating, i was very comprehensive and specific in my answer

Yes i covered that point

So you mean you tried all the combinations of insulation and compared the measurements, or you just did what you're suggesting and didn't notice any particular issue? The physics of the situation is fairly well understood, heat in has to be greater than heat out. Thermal mass to be considered. And the dew point and humidity need to be taken into account.
Balance heating, ventilation and insulation and you'll be sorted, although less heating would be cheaper and more insulation would be warmer.

Not getting into an argument with you.... That's pointless

The physics of it all are simple - heat lost via ceiling is around 45% (depending on which gauge you use). Heat lost via walls is around 20% (depending on which gauge you use).

Heating a room with an adequate radiator is faster. Using underfloor heating is slower.

(Depending on which system you use, gas (central heating) is cheaper than electric (underfloor heating))

In a perfect world, you would have insulated walls, floors, ceilings as well as underfloor heating, radiators and any other features required. Logically though, it's better to go with insulating the roof and using an adequate radiator as this gives you the best heat output as well as the best heat retention within the room.

Real life scenarios - depending on the size of the house etc, you'd have to switch you underfloor heating on much earlier than your centrally heated radiator to warm the entire bathroom up.

If money is no object then by all means insulate everything - that will deffo give you the best results. But if there is a budget, you're better off going for the insulation in the roof and an adequate radiator - I can see from the pic though that this will be difficult because of your roof structure.

I'd go with the celotex type of insulation in the eves if it can be fitted in there and then standard loft insulation above the rest of the bathroom. Again, if you have the money, go for the wall insulation too it will help, just not as much as the ceiling insulation.

 

[JP_]

50mm kingspan (or similar) on the external walls, check ceiling space is fully insulated to edges too.
I'd stick the insulation to the walls with everbuild pinkgrip foam, tape everything up with silver insulation tape. Need to tape up otherwise moisture will get through and condense on the cold side, causing mould and rot problems.
Then stick boards over.

Cold spots will lead to condensation and mould. My bathroom currently gets mould along the ceiling near the outside wall where there's not enough insulation in the loft (I plan to fix very soon...)

 

[wwwebber]

In our previous house we used 50mm insulation backed plasterboard dobbed and dabbed directly onto our 9" thick external walls not only in the bathroom but throughout - got rid of cold, noise & damp. No cold spots and nice and warm.

 

[Don8]

Thanks all, think we'll insulate the walls then. I'll speak to the builder to see what he thinks about the ceiling. Not expecting much heat from the UFH just something to take the edge off the tiles in the morning, it's not expensive. Main source of heat will be a towel rail, will go with a large one with a decent BTU output