Underfloor insulation choice between concrete and PIR with costs

Yellowmac

Would really appreciate the opinions of the experts on this forum.

If you were doing a 70-80k renovation on a (cold) 1960s house (new kitchen, new rear windows, updating gunbarrel plumbing and wiring throughout) and you are taking up all downstairs floors to add insulation would you go for

Option A. 100mm PIR insulation between joists, fit 18mm osb 3 sheets to existing joists 12,200 euro.

Option B. Insulated concrete floor slab, radon barrier 21,500 euro.

Floors are suspended 300mm. Main goal is warmer/less drafty. Not going for underfloor heating. Builder advises both are similar jobs in terms of time/labour and mess but a better (warmer) outcome from the concrete.

Struggling to decide whether it's worth the 9k extra. Thanks for any thoughts.

BenIrishHome

If you are doing all that, I dont know any builder that would suggest not doing the concrete slab AND underfloor heating.

You only get one chance to do this, might as well do the whole hog.

Yellowmac

Thanks for the reply. He did initially quote us for UFH too. We were thinking not to get it because we heard its expensive to run, the house is not insulated that well otherwise. But appreciate the feedback and advice

Alkers

They're both mad money which you'll never recoup in terms of energy savings.

You could diy the first option, particularly as the floors will likely be lifted in any case to do the plumbing and wiring.

I would do neither at that money and spend on EWI instead.

Yellowmac

Thanks appreciate the feedback on the costs

jonnybravo

We did the second option with underfloor heating (but we also added external insulation). It's a great job and house is very comfortable. Underfloor heating comes on for a couple of hours in the morning and stays warm for the rest of the day. Lived in a house with suspended floors before and would never do it again. Just no comfort in it.

Yellowmac

Thanks for reply, good to know you had a good outcome with the concrete and UFH!

Yellowmac

Thanks for replies so far.

Our initial reason for lifting the floors was mainly to replace the old piping/plumbing system, it's only because they're coming up anyway that we saw the chance to insulate underneath and we were wondering what option would give us a warmer return.

SC024

Concrete & underfloor heating if you can afford…

Idbatterim

Hang on, have you gotten more than one price for this work ?! It's not exactly like it's going to be a nice job to do in future or prices will drop... the house won't qualify for the vacant or derelict homes grant ?

Alkers

You could just go with the airtightness measures outlined in the below if you're reluctant to spend also.

https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors?srsltid=AfmBOooYbYQs9HfO5mQZZPkLgoBmx9m6GuyPYXynixjcsdW9MuLGaSGC

Calahonda52

https://www.boards.ie/discussion/comment/123057167#Comment_123057167

There is a lot of work in that approach and is difficult to get right and I have yet to see any contractor that has the patience to do it right, especially where the last floor joist is // to wall and where joists may penetrate the inner leaf of the external walls.

Then the question remains about make ing the whole thing A/T for the new pipes and existing cables, especially 2.5 sq and bigger if any

Yellowmac

https://www.boards.ie/discussion/comment/123057167#Comment_123057167

Thanks for that suggestion, that's interesting and actually that link to the article is helpful for me to understand the floor draft issue.

I think with our project timeline our only 2 options really are the 2 the builder gave us. In terms of getting the project finished within the planned time frame.

Yellowmac

https://www.boards.ie/discussion/comment/123056146#Comment_123056146

No we've only been quoted by our builder who's doing the overall project for us. The idea of insulating only came up because we are lifting the floors anyway as part of the replumbing works and it seemed mad to put new floors back down without doing anything to address drafts/heat/energy. We are acknowledge realistically that this insulation won't save us much on energy costs as someone said above, we mostly just want to feel a bit warmer!

No derelict grants unfortunately, we already live in the house it's just got some older components. Thanks for the suggestions.

Calahonda52

re

We are acknowledge realistically that this insulation won't save us much on energy costs as someone said above, we mostly just want to feel a bit warmer!

that post was BS but I won't engage with that sort of stuff its not about a narrow focus on U value energy saving.

There is much more to it than that

Am all done here

BenIrishHome

We're going to retrofit a 2001 dormer bungalow, that is supposedly a C1 but absolutely freezing especially our floors.

We have been quoted about €90k for total fit, incl A2W heat pump etc. less about €25k in grants.

That didn't include any UFH or changes to the flooring. We know if needs something, we're going to be replacing the awful old tiles and wood floor anyway so wanted the UFH.

First they quoted us €42,000 for UFH in downstairs (about 130 sqm) to dig up all floors. Huge price and very disruptive. Instead I found this concrete milling technique that cuts the routes for the UFH pipes into your existing floors, and the tiles just go down on top of it. No need to digg out the whole place.

At first our assessor was skeptical but they contacted these guys and worked out it was a good idea. Because we are 2001s build we probably have SOME PIR insulation under the slab (maybe 50mm not the recommened 150-200mm). But enough we wouldn't leak heat downwards too excessively. I'm hoping we can use nighttime rates and solar+battery to keep that floor slab warm as a heat store throughout the day. The new quote was €24,000 - still alot but worth it.

In a 1970s bungalow you need to take up the floor, and pour new concrete, you might as well add UFH. It won't add a huge cost in the grand scheme of things and its your one chance to do it. It really is the best consistent heating.

Idbatterim

https://www.boards.ie/discussion/comment/123058108#Comment_123058108

Ok,I would get another price or two, for this work personally. To get an idea if what your builder is quoting, is reasonable or not. Youre not his mate, I wouldnt care less with these serious sums , how he would take it, you arent taking away work from him, that you have agreed to… Are you getting new floors put down, laminate or tiles etc on this floor? Where I am going with this is, it is likely absolute madness, to not do the job… Even if that means, dropping costs in other areas, that can easily be done later, this cant…

MicktheMan

https://www.boards.ie/discussion/comment/123058697#Comment_123058697

€90k retrofit of a dormer bungalow… please say that they have tested for air tightness, put a robust plan of attack in place including a re-test when done to prove the works.

BenIrishHome

https://www.boards.ie/discussion/comment/123060224#Comment_123060224

no, funny enough they were recommending only manual vents which didn’t require air tightness test. I’ve asked them to add the MVHR system to the quote. Another €9k (€6k after grant). Will include a before and after airtightness test.

My big problem is - the heat just drops in the house as soon as the boiler turns off. So we’re leaky right? So surely I need to get all these always-open vents shut off, and then a system to deal with the moisture. Manual vents seem stupid.

Of course i need better attic and wall insulation. But to do all that plus UFH, why would I not do the MVHR?

of that €90k, about €25k was attic insulation and “sloped roof” insulation. Ie taking down all the attic plasterboard and putting in new thicker warmboard. Huge job, expensive. Is it worth it? Not on its own. We might be doing a couple of dormers up there so taking apart the inside roof, so might as well do the new warmboard, but I’m in two minds. Feeling this is the one area I might be getting shafted by the OSS, might see if a local attic insulation company would do me a better price.

MicktheMan

My big problem is - the heat just drops in the house as soon as the boiler turns off. So we’re leaky right?

So what's their plan on for air tightness then?. Am I right to conclude that the OSS came up with a €90k plan to address horrendous heat loss in the absence of an air tightness test … in a dormer. Your house is likely losing heat at a rate of knots (pun intended) because of a lack of air tightness, not a lack of insulation.

These OSS outfits exist because "Hey, there's a government backed grant for it so it must be good, right?

It's crazy what's going on and allowed to go on.

In my experience if you were to take, say, a fifth of that amount, you would have change in your pocket and a changed house if you were to ignore grants, OSS's etc and concentrate on addressing the real cause of your heat loss and improving both your comfort levels and your indoor air quality.

BenIrishHome

https://www.boards.ie/discussion/comment/123064151#Comment_123064151

You're probably not wrong. I have done enough projects in the past to probably PM my own retrofit, and DIY some of it too. Just with busy life and kids and stuff sometimes you want it off your hands.

There are a couple of areas it seems beneficial to use the OSS:

• Windows and Doors - only OSS can get you a grant for windows and doors. They reckon about €5,600 in grants on €25k of doors. That sounds alot but its approx. 15 windows including some big bay ones, a new front door and a big bifold unit to the kitchen.
• Air Pump Install - Good grants on this and they install it themselves.
• Solar - likewise, these guys do their own solar installs. If they had an outside contractor I would shop around. Fairly good quote of €10k on 14 panels (6kw system)

Their 'plan' for airtightness was mostly windows and doors and "additional draughtproofing" which was only about €1500, probably just sealing up around attic hatches etc (we do have 4/5 of these including into the eaves spaces)

I agree with what you are saying. Surely its draughts letting the heat out. But I'm walking around looking at vent after vent in every room. 1 in each bedroom, two in living room and 2 in kitchen, all the bathrooms etc. They're just open holes to the outside. I never feel drafts or wind from them but probably because all my lovely expensively warmed air is streaming out. Hence me convincing them i definitely need MVHR.

You have me starting to think i can do this myself now…

MicktheMan

https://www.boards.ie/discussion/comment/123064692#Comment_123064692

You have me starting to think i can do this myself now…

You probably could if you have both the skills (competent diyer) and the knowledge of the why, the what to do and the where. The former you either have or don't and a proper heat loss survey (note: not a BER) will supply the latter.

A significant number of my clients decide that they have (or they know someone close to them who have) the skills to do the majority of the work themselves.

But I'm walking around looking at vent after vent in every room. 1 in each bedroom, two in living room and 2 in kitchen, all the bathrooms etc. They're just open holes to the outside. I never feel drafts or wind from them but probably because all my lovely expensively warmed air is streaming out.

Perhaps try the following test yourself the next time it's anyway windy / cold outside. Temporarily seal all your wall vents for say 24 hours and see if this make a noticeable difference to you heat loss / retention.

I'm not saying the 'hole in wall' vents are good but merely questioning your thought process that they are a major issue for heat loss.

BenIrishHome

https://www.boards.ie/discussion/comment/123065869#Comment_123065869

You were the one who sumised that draftproofing was more important than insulation. Especially in a notorious dormer bungalow. Are you saying there are other areas where drafts/leakage is going to be worse than the vents? Can't just be attic hatches. tbf my 25 old double glazing is probably half the problem.

MicktheMan

https://www.boards.ie/discussion/comment/123066867#Comment_123066867

You were the one who sumised that draftproofing was more important than insulation.

Not sure what your point is here.🤷‍♂️

Are you saying there are other areas where drafts/leakage is going to be worse than the vents? 

Yes, likely pretty much, but every house is different to some extent. I'm not saying that the vents are not contributing but they are likely not as big a contributer as you might think. Similarly for your windows possibly. Most attic hatches are definite improvement opportunities especially the ones into the crawl space in dormers … think of these as external doors! But there are nearly always other aspects that are a complete surprise to the home owner when pointed out.

An air tightness test (as part of an overall heat loss survey) would be the best place to start to understand where the predominant issues are and how to resolve etc.

Yellow_Fern

€90k seems an emormous cost. A lot of that cost wont make your house more comfortable like a heat pump. As the other poster writes, get a good airtightness survey, lift flooring to solve airtightness and because you have a bungalow, you can potenially install mvhr to each room very easily. You could potenially make enormous improvements without even spending €15k.

BenIrishHome

Do you mean not doing the heat pump and stay with my gas boiler? That’s probably the major cost. But I have an EV and a good roof for solar, so seems like the next step to go off the gas entirely.

The attic does need better fibre insulation and I can do air tightness. I’ve been researching MVHR and they seem quite good, also I could DIY 90% of that.

I need new doors and windows and we’re doing a small rearrangement of the layout so we might as well do the whole job while we are at it. UFH is a must have for me and would suit this house, so that gets me back full circle to needing a heat pump for that slow and steady gentle heat.

Martee

Grappling with similar pickles at the mo. If looking at splitting out works from OSS keep in mind the qualification requirements to use one inc. min uplift in BER and max existing BER.

GreeBo

EWI with an uninsulated, suspended timber floor is not going to leave you with a "nice" warm house feeling IMO. If the floor is cold and draughty then the house wont be comfortable, no matter what else you do on the walls, roof.

If you are gutting the house then now is the time to do it all IMO. It will be unlivable during any of this, so you wouldnt want to do it twice.

Concrete floor with underfloor heating.

Strip the walls back to blocks and add insulation + air tightness membrane, VCL.

Same for the ceilings.

monseiur

https://www.boards.ie/discussion/2058388447/underfloor-insulation-choice-between-concrete-and-pir-with-costs

Definitely go for option 'B' if your budget allows. As you are replacing the back windows, and all rads are down consider dry lining the inside of ''external'' walls with say 50mm insulated plasterboard and upgrade attic insulation to at least 300mm. Contact SEAI there are good grants available for heating upgrades, insulation upgrades etc.

Alkers

https://www.boards.ie/discussion/comment/123090779#Comment_123090779

I don't think it will be as bad as you you let on.

You can still draught-proof the floor without insulating it. Then a good underlay and carowr which you'd likely do anyway. The ewi will extend below floor level also.

I know it's far from perfect, but at 20k, even if it meant the house was free to heat, it would take 20 years to pay itself back!

GreeBo

https://www.boards.ie/discussion/comment/123092129#Comment_123092129

It might be possible to make it draught proof (which, as pointed out before, is very hard to do unless you are doing it yourself), but it will still be cold.

If you just look at cost vs payback you could spend nothing on heating ever and save loads. Your life will be miserable and uncomfortable but you will "save" money.

Doing the 20K work will immeasurably improve your standard of living and enjoyment of the house.