Suspended timber floor to Limecrete or something else?

[Aaron83]

Hi all, hope we're keeping well.
I was all-in on replacing the suspended timber floor in our 1930's (with 9 inch think, solid brick walls) semi-detached home, with a Limecrete floor. Due to it both insulating the floor and providing a thermal store for the UFH within it.

THEN, I had a very helpful visit from @Lacan07 (thanks so much again for your time), who planted the seed of whether or not a Limcrete floor was worth it due to our house (we think) having a DPC (photo attached of thicker mortar line on bottom edge of airbrick), as well as the the LCF costing so much.

So I'm wondering what peoples thought are on our best options.

Many thanks!

 

[Cubist]

I'm biased in favour of timber and my attitude is one of 'If it aint broke don't...'

Given that, and assuming theres nothing catastrophically and structurally wrong with the existing floor I would favour only new floorboards perhaps. Unless there was a very strong thermal and economic argument in favour of going down the limecrete avenue.

 

[Aaron83]

I'm biased in favour of timber and my attitude is one of 'If it aint broke don't...'

Given that, and assuming theres nothing catastrophically and structurally wrong with the existing floor I would favour only new floorboards perhaps. Unless there was a very strong thermal and economic argument in favour of going down the limecrete avenue.

Thanks for the advise Cubist.

I don't think there's any structural issues with the floor, but we find it very drafty + cold (as you'd expect) and would really like UFH. Hence limecrete became an obvious option - I liked the promise of great moisture management/breathability with us having solid brick walls, as well as other characteristics.

We're open to any option that's a solid long-term solution.
Somone suggested a mix of insulating between the joists, then pouring in a "standard" screed over the top, to fulfil our wish of having both an insulated floor with a thermal store for the heat created.
It just didn't sound right to me - granted I'm no expert .

 

[Cubist]

I have no idea if some of these hybrid and seemingly 'off the wall' floor insulation ideas are at all effective but I would respect Lacan's opinion regarding a well designed limecrete floor option as I believe that such would not compromise the houses need to breathe effectively.

 

[Lacan07]

Everyone on here knows I'm no fan of solid floors in old houses, even with limecrete which is after all usually NHL5 - i.e, very strong and not massively breathable.

My argument is Aaron can insulate his suspended floor with PIR and still have his UFH for far less cost and disruption than a new limcrete floor. The question is will the superior mass of a limcrete floor justify the extra cost and indeed translate into significant savings on his heating bills.

 

[Lacan07]

@Aaron83

Just wondering if you were aware of the Green building forum?

Might be worth joining and asking the question there too, they tend to specialise in matters of insulation. Some of them are quite obsessive.

Here's the link:

www.greenbuildingforum.co.uk

 

[aockenden]

@Aaron83

Just wondering if you were aware of the Green building forum?

Might be worth joining and asking the question there too, they tend to specialise in matters of insulation. Some of them are quite obsessive.

Here's the link:

www.greenbuildingforum.co.uk

I thought they were shutting down this year?

 

[Aaron83]

@Aaron83

Just wondering if you were aware of the Green building forum?

Might be worth joining and asking the question there too, they tend to specialise in matters of insulation. Some of them are quite obsessive.

Here's the link:

www.greenbuildingforum.co.uk

Thanks @Lacan07 !
Much appreciated

 

[Aaron83]

I thought they were shutting down this year?

Sadly, does look like it.

 

[Kearn]

the approach of a limecrete floor system can be achieved for less cash, albeit still a decent chunk. the bit that really matters, is the the RFG sub-base - Glapor or which other brand name,,, its a capillary break, solid, lightweight, insulating... the first and last are the most important really.

the slab on top is largely a matter of choice. NHL 5 is by all accounts harder than concrete after 5-10 years. NHL 2/3.5 still cosst way more than a concrete slab. heresy, I hear... but the limecrete slab doesn't really perform a role in this system and if you're on decent terms with any of the major lime suppliers, they'll tell your as much. the limecrete slab isn't breathing or moisture managing - the RFG prevents ground moisture reaching the slab. if you follow the rules, a perimeter break of cork does similar from the walls, although its termed an expansion requirement or something. the limecrete slab is also certianly not flexible or dealing with movement in the building.

so the hybrid system is RFG sub base, nicely compacted and give more space if it is limited, to this element, then add a concrete slab over, with wet UFH, or not.

there is a UK based supplier of RFG imminent, which will I'm told be bringing the price down noticeably....

 

[Lacan07]

I thought they were shutting down this year?

I wasn't aware of that, I know its a small subscription. They helped me considerably in the early days, especially Tony who I think published a book recently.

 

[Aaron83]

Thanks so much for the great info/health @Kearn, really appreciate it.

So in short, compacted RFG (wrapped in membrane) + concrete + UFH&Screed (with the concrete & screed having a cork perimeter, should be fine (and cost less than the full Lime alternative).

If so, this really does seem like a great alternative as it'll (hopefully) cost less (keeping the grey away until the next bill comes in ) and give us the (albeit, slower) thermal store for the UFH, I was hoping to incorporate .

Two final queries I have with such a floor (for both myself and the builders I am looking to contract as they're totally new to RFG etc.). 1) Am I right in thinking none of this (internal) floor, should end up above ("bridge") the level of our DPC?
& 2) once the floor is in, are the air-bricks still needed or can they be bricked up?

Thanks again for all the help

 

[Kearn]

Thanks so much for the great info/health @Kearn, really appreciate it.

So in short, compacted RFG (wrapped in membrane) + concrete + UFH&Screed (with the concrete & screed having a cork perimeter, should be fine (and cost less than the full Lime alternative).

If so, this really does seem like a great alternative as it'll (hopefully) cost less (keeping the grey away until the next bill comes in ) and give us the (albeit, slower) thermal store for the UFH, I was hoping to incorporate .

Two final queries I have with such a floor (for both myself and the builders I am looking to contract as they're totally new to RFG etc.). 1) Am I right in thinking none of this (internal) floor, should end up above ("bridge") the level of our DPC?
& 2) once the floor is in, are the air-bricks still needed or can they be bricked up?

Thanks again for all the help

The cork seems to be only really added as a moisture break. So in your situation, it may actually be useful. I hadn’t twigged you had a DPC - are you now certain?

Instinctively I’d say keep the floor beneath the DPC to prevent bridging, but that wouldn’t make any sense as undoubtedly your internal floor would be way too low.

I would think that if the RFG bridged the DPC it may not be so bad, as the moisture should remain in the lower 1/3 or so.

Air bricks are redundant- only useful for a suspended floor.

 

[Aaron83]

Thanks again @Kearn.

The DPC hasn't been confirmed (I will ask the builders next time they're over), but it does look like one (to my untrained eye) and I think @Lacan07 said it looked like one when he came over (I've attached a pic to the first post on this thread if you'd like to have a look?).

 

[larry]

Completely mad idea but how about using something like porcelain tiles (impervious) to "bridge" the DPC? If fixed on the top and bottom only with one half above the DPC and the other half below then the height of the tile could presumably give you a bit of extra room to go up or down without actually creating a bridge.
Forgive me if this is cobblers but just a thought.

 

[mardinor]

How about a big rug, or carpet? And you can crack the heating a little higher for many years before you offset the embedded carbon in any mods you make, I'd wager.
Just a contrarian perspective!

 

[Lacan07]

Thanks again @Kearn.

The DPC hasn't been confirmed (I will ask the builders next time they're over), but it does look like one (to my untrained eye) and I think @Lacan07 said it looked like one when he came over (I've attached a pic to the first post on this thread if you'd like to have a look?).

I wasn't entirely sure to be honest Aaron, if memory serves what you pointed out was below the air brick. I would have expected to see it above. I'm pretty sure your house must have a DPC but perhaps not where we were looking.

 

[Aaron83]

Yep, that sounds more like what you said @Lacan07 , my memory ain't the best mate - sorry .

That's interesting about you thinking that thick mortar line likely isn't the DPC - in all honesty, I just assumed it was due to most (albeit newer) houses DPC's I've seen having more prominent mortar lines (with the plastic sheet going through the middle).

Does anyone know how to confirm it (or where) our DPC is?
Will the photo (or a more detailed one) suffice, or would I (or a pro) need to physically check something?

Thanks again @Lacan07 , all.

 

[Lacan07]

Yep, that sounds more like what you said @Lacan07 , my memory ain't the best mate - sorry .

That's interesting about you thinking that thick mortar line likely isn't the DPC - in all honesty, I just assumed it was due to most (albeit newer) houses DPC's I've seen having more prominent mortar lines (with the plastic sheet going through the middle).

Does anyone know how to confirm it (or where) our DPC is?
Will the photo (or a more detailed one) suffice, or would I (or a pro) need to physically check something?

Thanks again @Lacan07 , all.

Yes you may well be right, it's not something I was aware of. I would expect to see it above the airbrick though. How old is the house again, early 20th century? You could do a bit of exploring by scraping away a bit of mortar. It's easily replaced.

 

[Aaron83]

Yes you may well be right, it's not something I was aware of. I would expect to see it above the airbrick though. How old is the house again, early 20th century? You could do a bit of exploring by scraping away a bit of mortar. It's easily replaced.

Yep, it's a 1930's built house.

I'll do some reading online to see if there's anything on it, and if not, and no one here can advise, have a look myself as a last resort (only due to my lime pointing being the opposite of top-notch ).
Thanks.