Combining Internal & Cavity Insulation

rob w

I am living in a house with cavity insulation already installed by previous owners, however the house is still quite cold - most likely from draft coming through suspended floor on ground floor level - and this will be insulated at some point in future.

However, we will be renovating the downstairs shortly and was planning on battening out the walls and installing new plasterboard on these battens. Is there any reason I couldn't or shouldn't put insulation on the external walls - either insulated slabs or insulation between battens - in combination with the existing cavity insulation?

I am just wondering is there the potential for any issues with thermal bridging/breathability/condensation on the external walls etc if combining CWI and IWI?

Thanks

BryanF

Deal with the floor first?
If you must do the walls, why batten? Use insulated slabs?

sydthebeat

deal with your draughts first, you might be surprised with the results.

What insulation (type and thickness) is in your cavity currently, and is there scope to upgrade this?

tedimc

rob w wrote: »

I am just wondering is there the potential for any issues with thermal bridging/breathability/condensation on the external walls etc if combining CWI and IWI?

I did this, but as others can attest to - it is not ideal. However, my options were limited as I only had a 75mm cavity.

In order to try to prevent condensation, I used a separate insulation board (foil both sides) as opposed to the insulated plasterslab. I then filled any gaps with expanding foam and then taped over it with foil tape. I started to use the plastic plugs, but they were next to useless.

I then put plasterboard on over the insulation. Total build up was 75mm of foam in the cavity and 80mm internal on walls. I forgot to say, walls were already plastered and skimmed on the inside, but in bad shape.

One word of caution with internal insulation - it's a pain to hang anything on of any weight - curtain poles,etc.

All said and done, very happy with the results. In now about 3 years, and no sign of any issues (fingers crossed!)

rob w

BryanF wrote: »

Deal with the floor first?
If you must do the walls, why batten? Use insulated slabs?

Thanks, I intend to deal with the floor first, probably around the same time as doing the walls though. No reason I must batten, insulated slabs are definitely an option too.

I am more concerned about whether any issues may occur insulating on top of a cavity insulated block wall? I am no expert on this but am aware of people having issues with condensation etc which I am just trying to avoid.

rob w

sydthebeat wrote: »

deal with your draughts first, you might be surprised with the results.

What insulation (type and thickness) is in your cavity currently, and is there scope to upgrade this?

Hopefully sorting the drafts will help alright!

It was previous owners who insulated cavity so not 100% sure of the type, from what I have seen it is a small grey (polystyrene maybe? ) bead that has been blown in to the cavity.

rob w

tedimc wrote: »

I did this, but as others can attest to - it is not ideal. However, my options were limited as I only had a 75mm cavity.

In order to try to prevent condensation, I used a separate insulation board (foil both sides) as opposed to the insulated plasterslab. I then filled any gaps with expanding foam and then taped over it with foil tape. I started to use the plastic plugs, but they were next to useless.

I then put plasterboard on over the insulation. Total build up was 75mm of foam in the cavity and 80mm internal on walls. I forgot to say, walls were already plastered and skimmed on the inside, but in bad shape.

One word of caution with internal insulation - it's a pain to hang anything on of any weight - curtain poles,etc.

All said and done, very happy with the results. In now about 3 years, and no sign of any issues (fingers crossed!)

Great, thanks for that feedback and advice. Our internal walls are wallpapered currently and I don't fancy stripping and making good, so will slab over them I think.

BryanF

keep dry lining(1/3) v cavity insulation (2/3)

Seriously tough spend the time and money on the floor first.
I’ve a few posts back along covering what I did, the suspended floor insulation and air-tightness work I did makes the room hold its heat the best in the existing house

Who2

My house originally had internal drylining it was pumped after maybe 10 years which created no issues that I seen, I put external insulation on about two years and to date I haven’t seen anything problematic, only I have to put in hrv as the house is far too sealed. Pipes are in, just the unit now. With suspended floors you have exterior vents which will be allowing your timbers breathe. Don’t just seal them up as it will cause your floor joists to rot if you do. You can lift the floorboards if your inclined and get a breathable foam filled done but if your going to that hassle I’d just rip them up all together and put in a dpc. High density insulation and pour a new concrete screed.

rob w

BryanF wrote: »

keep dry lining(1/3) v cavity insulation (2/3)

Seriously tough spend the time and money on the floor first.
I’ve a few posts back along covering what I did, the suspended floor insulation and air-tightness work I did makes the room hold its heat the best in the existing house

Great, I will have a look over those posts - how far back are they or can you link?

Thanks

BryanF

Use the search function, use key words etc

Also see gov advice at link below

https://www.nsai.ie/about/news/publication-of-sr-542014-code-of-practice/