What D&D insulatiuon to use on bathroom walls

[D_Evans]

Hi to you all, long time lurker here but first time poster.

I am renovating my 1st floor bathroom and looking to insulate the two brick walls, one exterior (cavity brick, no cavity insulation) and one party.

Although I was initially thinking of using stud work I am now thinking it would be simpler to use D&D with insulated plasterboard.

I’m a little lost on the ‘U number’ I need, and what would be the most cost effective insulation to use. I am also putting a shower in the corner against both the exterior and party wall, so any plasterboard I put in would need to be suitable for tiling and moisture resistence.

To complicate the matter slightly more - there is a false ceiling in the bathroom with an 80cm or so cavity above, with no insulation in it. I think the loft has insulation in the rafters however. I am not sure how or if this matters and if it has knock on implications.

Here is a pic of the room in question, any advice on how to proceed would be most appriciated!

 

[IT Minion]

To get to modern building spec you'd need something like 100mm of Celotex. But there is nothing saying you need to go that far. 50mm stuck to the brickwork with gaps foamed or taped and then plasterboard over that is probably a good balance between insulation, cost and reduced floor space.

Why insulate the party wall? It shouldn't make any difference to heat loss and Celotex is nearly useless for sound insulation.

Separate plasterboard and insulation is generally agreed to be easier to fit and cheaper.

You'd need to take the insulation up into the false ceiling, otherwise it'll let all your heat escape into the false ceiling gap and vanish above the insulation. Plus condensation risks etc.

 

[JohnD]

As you have the cavity open round that window, you might consider pushing insulation into it before you close and insulate the cavity. There will probably be cold air blowing around in it. Your brickwork looks pretty sound, but look for any wall defects or damp in the outer leaf. Draughts can also blow into the room from gaps in the brickwork below plaster level, especially around joist ends, which you can stuff with mortar, mineral wool, or expanding foam.

You can use dense mineral wool batts behind plasterboard to muffle party wall noise slightly, but it must be cellar to loft, including the space above the ceiling and below the floor. It will also help the room heat up quicker.

Cement board (like tile backerboard) is very much more resistant to damp than plasterboard.

 

[^woody^]

Just get any 30 or 60mm insulated plasterboard.

It's a bathroom don't forget, you'll be extracting almost all the air anyway, waste of time trying to insulate it. Ceiling insulation would be of more value.

You're better off using a cement board such as hardy backer for the shower area.

 

[D_Evans]

To get to modern building spec you'd need something like 100mm of Celotex. But there is nothing saying you need to go that far. 50mm stuck to the brickwork with gaps foamed or taped and then plasterboard over that is probably a good balance between insulation, cost and reduced floor space.

So are there no regulations I have to follow or adhere to for a self renovation like this? I had watched a YT vid where the guy sad his local building reg guy said if you are insulating more than 50% of a room during renovation then you need to get it signed off (maybe I (or he) got this wrong and the 50% is for the whole house?)

Why insulate the party wall? It shouldn't make any difference to heat loss and Celotex is nearly useless for sound insulation.

Honestly the main reason was that if I used D&D for the exterior wall then I may as well for the party, as I need some depth to hide concealed pipes and shower bits the insulation would provide this where board alone may not, but now you point it out it does seem needles if there is a simpler solution? (edit: now thinking of just using Marmox Multiboard for the whole room, cement board and some insulation as well)

Separate plasterboard and insulation is generally agreed to be easier to fit and cheaper.

So in the case of D&D do you just glue your choice of plasterboard to the insulation?

You'd need to take the insulation up into the false ceiling, otherwise it'll let all your heat escape into the false ceiling gap and vanish above the insulation. Plus condensation risks etc.

Cool, ok, I think that might mean taking out the false ceiling, but I'll see if there is any access from the attic.

As you have the cavity open round that window, you might consider pushing insulation into it before you close and insulate the cavity. There will probably be cold air blowing around in it.

Yes, I was having similar thoughts!

Your brickwork looks pretty sound, but look for any wall defects or damp in the outer leaf. Draughts can also blow into the room from gaps in the brickwork below plaster level, especially around joist ends, which you can stuff with mortar, mineral wool, or expanding foam.

You can use dense mineral wool batts behind plasterboard to muffle party wall noise slightly, but it must be cellar to loft, including the space above the ceiling and below the floor. It will also help the room heat up quicker.

Cement board (like tile backerboard) is very much more resistant to damp than plasterboard.

Do you mean I would have to insulate the entire party wall through the entire house? If so it's a little more work that I plan to take on, as the house may go up for sale or be rented in a year or so.

I also plan to fill in any voids with something such as expanding foam as well!

Re: cement board - thanks yea it was one reason why I was trying to figure out if I could just use D&D insulation then attach my own board. But if I don't need to achieve some u value for the room with a certain type of insulation, would something like Marmox Multiboard do the job? As it's cheap and would mean I could just D&D it to the wall and call it a day.

Just get any 30 or 60mm insulated plasterboard.

It's a bathroom don't forget, you'll be extracting almost all the air anyway, waste of time trying to insulate it. Ceiling insulation would be of more value.

You're better off using a cement board such as hardy backer for the shower area.

Thanks, I actually just asked above about Marmox Multiboard - I could happily do the whole bathroom with this to provide a little extra protection from any moisture, and it has thicknesses that are enough to conceal pipe and fittings as well as provide some insulation.

 

[JohnD]

Do you mean I would have to insulate the entire party wall through the entire house?

i had in mind more that if you just line the plastered parts of the walls (people often do this) the room will still get noise coming through the easiest route, which is the gappy, unplastered brickwork above the ceiling, below the floor, and behind the skirting. You can pack between the floor joists as well.I notice you have stripped the plaster, skirting and floorboards so this is a good time.

But yes, for best whole house results, do the entire party wall. You don't have to do it all in one go, you might do each room individually as you renovate.

I was once embarrassed when I lived in a terraced house and the neighbour asked about my cough, because they could hear through the bedroom wall.

Sometimes the noise is from neighbours who are noisy in the bedroom, and sometimes it's halls and staircases with elephants running up and down (this is harder because it's impact transmission, not airbourne).

 

[D_Evans]

Thanks, well I will insulate what part of this wall I can, and I'll defo keep this in mind for the other rooms as I do them.

 

[JP_]

I am doing this, and use 50mm kingspan stuck on with Everbuild pink dry fix foam, and then boards put over. I think I will use a tilebacker board for tiled areas.
There is a product (not used, not bought) called Marmox that some tile shops sell, which is like insulated plasterboard, but insulated tile backer board (also for external render etc). https://www.tilefixdirect.com/product/Marmox-Multiboard-Tile-Backer-Insulation-Boards#MX50MM

I think insulation is very important as without it, you will get condensation staying on those solid walls, which will turn to black mould in time. I had loads of mould problems in my old shower room (1930s 9 inch solid brick walls) but none at all in the new bathroom with 50mm kingspan (plus a high boxed in area stuffed with another 20cm rockwool insulation)

Also insulate the window reveals, even if you can only get 10mm in there.

I'd put a bit of insulation on the party wall too - if they have an uninsulated bathroom then you might still get cold spots and condensation. OK, less likely, but you have not control over what they do next door, so if there is room for 20-30mm insulated board then might as well use it.

 

[IT Minion]

So are there no regulations I have to follow or adhere to for a self renovation like this? I had watched a YT vid where the guy sad his local building reg guy said if you are insulating more than 50% of a room during renovation then you need to get it signed off (maybe I (or he) got this wrong and the 50% is for the whole house?)

25% of an external wall according to here. So it depends how big your bathroom is compared to the rest of the house. Even then it seems to be one of the building regs that doesn't get much attention, probably because it's lower on the threat-to-life spectrum than taking out structural elements or messing with fire escapes.

Even then, the regs don't say you have to get to current spec at all costs. If it'd be an unacceptable loss of floor space then less is ok.

 

[D_Evans]

25% of an external wall according to here. So it depends how big your bathroom is compared to the rest of the house. Even then it seems to be one of the building regs that doesn't get much attention, probably because it's lower on the threat-to-life spectrum than taking out structural elements or messing with fire escapes.

Even then, the regs don't say you have to get to current spec at all costs. If it'd be an unacceptable loss of floor space then less is ok.

Thanks, I have looked into it a little more, and the wording seems to suggests the 'wall' is the 'thermal element' that requires regulation if it's more than 50%, and it is (a you say) only where it is practical to do so. The bathroom wall is also no where near 50% (or 25 for that matter) of the external wall.

So it doesn't look like I need to worry about that, so defo leaning toward Marmot Multiboard now!

 

[mikeey84]

If you are tiling, make sure you use plenty of mechanical fixings with large washers.

I'm not sure I would trust just foam or just adhesive if I was adding a huge weight of tiles.

 

[D_Evans]

Thanks, I'm only tiling around the bath but I'll be sure to make sure whatever I use also as mechanical fixings, with a few extra for good measure around the shower area.