Underfloor insulation choice between concrete and PIR with costs

Alkers

https://www.boards.ie/discussion/comment/123093999#Comment_123093999

People have lived in these kind houses for years and were never miserable and uncomfortable.

I agree fully, the spend on heating will be more than not doing it, but not significantly so. There will be heat loss through the floor and associated drafts but it won't make the house miserable and unconfortable. It makes more sense to me to spend slightly more on heating each year than to spend 20k here as discussed.

Busman Paddy Lasty

Get rid of the suspended timber floor. It's well worth the €9k extra. Not about financial payback but comfort. Having a floor that feels warm in the morning barefoot.

Getting rid of drafts does improve comfort levels. You can run your rads at a lower temperature.

Paulzx

I had a similar choice a few years ago. Redo the suspended floor or concrete in the space. I did not want underfloor heating so this wasn't a factor in the equation. House is late 60's semi d. The price difference between both options was much less than your quote.

I went for the concrete floor. This included rebar, insulation and radon sump. Cost was about 9 grand.

I felt that it was the best way to rule out draughts and also problems with pests in the underfloor void. I have no regrets about the option i took.

I done a rewire and got rid of gun barrell plumbing as well

GreeBo

https://www.boards.ie/discussion/comment/123095425#Comment_123095425

It wont make the house miserable and uncomfortable, the house will remain miserable and uncomfortable at this time of year.

Its either roasting as the heat is on full blast or freezing cold 15 minutes after the heat turns off.

I am ignoring the cost of heating and purely looking at the comfort levels and enjoyment of the house. People lived in mud huts with open fires and a hole in the chimney for even longer than they lived in suspended floor semi D-s.

OP, if you can in anyway afford it, go the whole hog. If you cant afford to do that, I would wait until you can. Spend what you have on attic insulation etc. But don't spend 80 on a refurb instead of spending 90, that extra 10K will be meaning less in 5 years time but the insulated, heated slab will be the gift that keeps on giving.

Yellowmac

Thanks for all the replies, I really appreciate everyone's input and advice. We are going ahead with the concrete underfloor insulation throughout downstairs and drylining all downstairs external walls. Not getting UFH for other reasons.

It's less about saving on heating or return on investment of the cost of works, more about comfort level of the house.

The attic is currently partially insulated its probably a source of heat loss but we dont want to put much into insulating it more as as we'll be converting it in the next 3-5 yrs. I think between the floors drylining and attic, the house will be much warmer in the end.

The total reno is coming in at 68k of which 21k is under floor concrete- eek.

Thanks all

Yellowmac

1.

Busman Paddy Lasty

You won't regret it. Did the builder give you a spec for the floor materials?

We did 80mm screed. 150mm PIR insulation. Engineer was super strict on using an S.R. 21 aggregate underneath instead of any old rubble or other fill.

Yellowmac

https://www.boards.ie/discussion/comment/123102967#Comment_123102967

The only info I have is 100mm PIR between joists, he didn't say the screed, I'll check with him. Thanks for the info

Yellowmac

https://www.boards.ie/discussion/comment/123096137#Comment_123096137

Thank you, it's great to hear from someone who was in our position and is happy with the choice they made. I was also convinced by the fact that concrete would mean less vermin!! The floors are so drafty (find myself sitting on them often with small kids).

We are doing rewire and gun barrel too and it's also a late 60s semi d. Glad it worked out for you. We're hoping after this we'll never have to touch the house again!

Busman Paddy Lasty

https://www.boards.ie/discussion/comment/123103005#Comment_123103005

The floor joists are going in a skip shortly, so the 100mm insulation between them isn't an option anymore 😁

There are a few pros here that would surely help further if you throw up the builders spec for what they have priced.

Yellowmac

https://www.boards.ie/discussion/comment/123103057#Comment_123103057

Haha sorry I misread that from the quote for the other type of insulation, not the concrete. That will give you an idea how much I know about it all. Will get the specs and get some input on them, cheers

GreeBo

https://www.boards.ie/discussion/comment/123102900#Comment_123102900

3-5 has a nasty habit of turning into 5-10, even if you just bought some loft roll and lashed in on top yourself it would be worth it in my opinion.

Doing the drylining, floor and topping up the attic will make it a feel like a different house. I just did the same on a 1930s detached house, house is 21C all day everyday without worrying about draughts or open doors. (We did get MVHR, HP and underfloors done though :) )

Yellowmac

Sorry I have one last question, everyone here is very helpful and knowledgeable!

If we do drylining on all the downstairs external walls as part of this renovation, but don't touch upstairs. Are we opening ourselves up to any potential issues with cold bridges/damp areas. Where the insulated downstairs meets the uninsulated upstairs?

External bedroom walls seem to already have some amount of IWI done by previous owner (we suspect from knocking on them!) but it probably isn't the thickness that we'll be putting in om ground floors.

Thanks

hesker

A lot of people stating the importance of air-tightness and controlled ventilation which is of course true. However it’s not easy in the current setup where nearly all OSS flatly refuse to retrofit air-tightness measures and SEAI offer no grants for it or state any requirements for it.

GreeBo

https://www.boards.ie/discussion/comment/123111365#Comment_123111365

The problem with doing it partially is that the warm, damp air that currently puts a little condensation on all the walls, will now put the same total condensation, but on fewer walls, making it more of a problem.

e.g 1L of water spread over every external wall is hardly noticeable, 1L on 1 wall is a potential problem.

If you are double/triple glazing downstairs but not upstairs its going to be the same problem, but magnified by dripped windows and wet window sills.

I'd buy a dehumidifier and stick it on the landing, to try to cut down on condensation problems, for a couple of hundred quid thats a no brainer for me.

Yellowmac

https://www.boards.ie/discussion/comment/123111593#Comment_123111593

OK thanks that's very helpful. Will invest in a dehumidifier for sure