Softening the feel of a concrete slab floor

[Sparrowhawk]

We currently have a suspended wood floor covered with engineered wood downstairs in our 1930s house. Because we'd quite like underfloor heating and there isn't much space to insulate under them without excavating down a bit, one idea we're toying with is replacing the floor with an insulated concrete slab. There may be 100 reasons this is a bad idea but assuming it's workable...

 

We walk around in socks or bare feet for most of the year. We like the slight springyness of a suspended timber floor underfoot, especially when exercising.

 

I've lived in rented houses in the past with concrete floors with thin carpet and poor underlay and the hardness is noticeable. We'd want to use laminate or engineered wood and with UFH I think underlay would get in the way of transmitting heat? So - are there any ways to make a concrete floor feel less like you're walking barefoot on a driveway?

[JohnMo]

There is a big difference between a concrete floor and a concrete floor on top of a couple hundred mm of insulation.  The insulation adds some give, so much so that a fell of some steps on to my bum, from a few feet up.  Apart from the shock, I got up and carried on working.  That would not be the case with just concrete.

 

It's not soft, but it's not super hard either.

[Gus Potter]

1 hour ago, Sparrowhawk said:

We currently have a suspended wood floor covered with engineered wood downstairs in our 1930s house. Because we'd quite like underfloor heating and there isn't much space to insulate under them without excavating down a bit, one idea we're toying with is replacing the floor with an insulated concrete slab. There may be 100 reasons this is a bad idea but assuming it's workable...

 

We walk around in socks or bare feet for most of the year. We like the slight springyness of a suspended timber floor underfoot, especially when exercising.

 

I've lived in rented houses in the past with concrete floors with thin carpet and poor underlay and the hardness is noticeable. We'd want to use laminate or engineered wood and with UFH I think underlay would get in the way of transmitting heat? So - are there any ways to make a concrete floor feel less like you're walking barefoot on a driveway?

Good for you and good thoughts!

 

For a bit of context I have been experimenting with different solutions over the years. First go was on a self build with suspended timber floors some 30 years ago. It worked mostly.. but lets say I could have "done better" as I did not know then what I know now.

 

I have to say.. this sort of thing crops up in my day job from time to time and I don't experiment on my Clients.

 

I have been doing up my own ex council house. I added an extension, laid some hard core, insulation, DPM and then a 100 mm thick concrete slab with A142 anticrack mesh... yes it is still the structural slab. I tied the wet UF heating pipes to the mesh. Then laid a layer of I think about 3.0 mm thick foam and floated a good quality engineered flooring over the top. I wanted a floating floor as opposed to glueing it to the concrete so I can lift parts if it ever get damaged, say by water or me doing something daft.

 

It has the give..and a bit of a spring.. me too am a big fan of bare feet in the house and a massive fan of UF. If you have a leather sofa then it's warm when you sit down as heated from below.

 

In another part I had the old timber suspended floor. Existing joist depth is 150mm. What I did was to get 50 x 50 timbers and fix to them 100 - 120mm wide rippings of OSB with plenty glue. The solum space is tight so then put plenty glue on top of the 50 x 50 (OSB on the bottom side) pilot drilled the joist at an angle and cheek screwed the 50 x 50 from above to pull it up hard against the underside of the joists, leaving a 150 mm ventilation space under. I had to do it this way as there is not enough room below the joists to a battery drill in to screw from underneath.

 

Now I had a 200 mm effective depth of joist with a ledge of OSB protruding. I then cut lengths of OSB nearly the width of the space between the joists and dropped them in so they rested on the OSB ledge. Next I cut 150mm PIR and fitted it tightly in between the joists. I went round any gaps with foam and then use silicont to really seal between the insualtion and the joists. Fixed to the insulation was the UF pipes, then a pug mix then the chipboardd flooring.

 

This is to be a bathroom so from BH have been following folk like @nod and plan to use a decoupling matt for large format tiles. Going to have a stab at laying these myself.. if it goes well will let you all know.. if not.. maybe not.

 

Now the down side of me renovating/  preparing an existing supsended floor was that is was very time consuming and to do it right requires a lot of attention to detail that a builder may not be that keen on. In other words it a great way for Build hubbers as a DIY project.

 

Now technically I know that the foam layer is an insulating layer that reduces the effectiveness of the UF. But I took the view.. the heat has to come out eventually. In both cases I put extra perimeter insulation around the edges.  Pratically I have learnt that it's a good idea to over spec the UF by way of closer pipe centres or larger diameter pipes, does not cost a lot. Reason is that my wife is a big fan of rugs and designer stuff. These rugs and their insulating effects far outwiegh my 3.0mm bit of foam.

 

@saveasteading has got a lot of info and knowledge about this so have a look at past posts. He also knows a lot about perimeter insulation and how it can really improve the heat loss performance.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Iceverge]

Time over again I would avoid a concrete floor. 150mm concrete plus 200mm EPS here. 

 

We have some with LVT and some with good carpet and thick underlay. Mainly to keep things as soft as possible but you know it's still down there.  As it's a passive standard house the floors never get cold. They're don't have that nice warm UFH touch, but they don't suck your will to live out through the soles of your feet either. Socks are the normal order of the day with no complaints.

 

I gather from those who run low temp heating in low energy houses that you don't get a hot UFH under foot feeling either. Please write in with the answers subscribers ?  @joe90 @TerryE @IanR@JohnMo to name a few. 

 

@ProDave has a screed over an I joist floor from memory. Does it chip a little bit off your spine every time you take a step like concrete floors? 

 

@JohnMo has recently put UFH over insulation below 2 x layers of OSB floating. I am very interested in this approach. No wet trades. No crucifying hammering of your joints.   

 

Another (slightly hippy) idea is an adobe (earth) floor.  A shed in my parents house had a floor of exposed earth. It was a lovely surface. Similarly in a garage workshop near me there's an area of 2m2 near one of the car lifts where about 60mm of earth has become congealed after falling off car's over the years and got too stiff to be brushed out. Everyone stands on it subconsciously while shooting the breeze. 

 

 

 

 

[nod]

39 minutes ago, Gus Potter said:

Good for you and good thoughts!

 

For a bit of context I have been experimenting with different solutions over the years. First go was on a self build with suspended timber floors some 30 years ago. It worked mostly.. but lets say I could have "done better" as I did not know then what I know now.

 

I have to say.. this sort of thing crops up in my day job from time to time and I don't experiment on my Clients.

 

I have been doing up my own ex council house. I added an extension, laid some hard core, insulation, DPM and then a 100 mm thick concrete slab with A142 anticrack mesh... yes it is still the structural slab. I tied the wet UF heating pipes to the mesh. Then laid a layer of I think about 3.0 mm thick foam and floated a good quality engineered flooring over the top. I wanted a floating floor as opposed to glueing it to the concrete so I can lift parts if it ever get damaged, say by water or me doing something daft.

 

It has the give..and a bit of a spring.. me too am a big fan of bare feet in the house and a massive fan of UF. If you have a leather sofa then it's warm when you sit down as heated from below.

 

In another part I had the old timber suspended floor. Existing joist depth is 150mm. What I did was to get 50 x 50 timbers and fix to them 100 - 120mm wide rippings of OSB with plenty glue. The solum space is tight so then put plenty glue on top of the 50 x 50 (OSB on the bottom side) pilot drilled the joist at an angle and cheek screwed the 50 x 50 from above to pull it up hard against the underside of the joists, leaving a 150 mm ventilation space under. I had to do it this way as there is not enough room below the joists to a battery drill in to screw from underneath.

 

Now I had a 200 mm effective depth of joist with a ledge of OSB protruding. I then cut lengths of OSB nearly the width of the space between the joists and dropped them in so they rested on the OSB ledge. Next I cut 150mm PIR and fitted it tightly in between the joists. I went round any gaps with foam and then use silicont to really seal between the insualtion and the joists. Fixed to the insulation was the UF pipes, then a pug mix then the chipboardd flooring.

 

This is to be a bathroom so from BH have been following folk like @nod and plan to use a decoupling matt for large format tiles. Going to have a stab at laying these myself.. if it goes well will let you all know.. if not.. maybe not.

 

Now the down side of me renovating/  preparing an existing supsended floor was that is was very time consuming and to do it right requires a lot of attention to detail that a builder may not be that keen on. In other words it a great way for Build hubbers as a DIY project.

 

Now technically I know that the foam layer is an insulating layer that reduces the effectiveness of the UF. But I took the view.. the heat has to come out eventually. In both cases I put extra perimeter insulation around the edges.  Pratically I have learnt that it's a good idea to over spec the UF by way of closer pipe centres or larger diameter pipes, does not cost a lot. Reason is that my wife is a big fan of rugs and designer stuff. These rugs and their insulating effects far outwiegh my 3.0mm bit of foam.

 

@saveasteading has got a lot of info and knowledge about this so have a look at past posts. He also knows a lot about perimeter insulation and how it can really improve the heat loss performance.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If you are fixing matting to timber Use Ardex Absolutely Bombproof 

[joe90]

27 minutes ago, Iceverge said:

I gather from those who run low temp heating in low energy houses that you don't get a hot UFH under foot feeling either. Please write in with the answers subscribers ?  @joe90 @TerryE @IanR@JohnMo to name a few. 

Yes our UFH keeps the house at a stable temp but no “hot” floors.

[saveasteading]

2 hours ago, Sparrowhawk said:

with UFH I think underlay would get in the way of transmitting heat?

We've just fitted carpet on ufh.*

Special underlay has a large proportion of gaps. Then the carpet must also be open textured.

For laminate I don't know how this can be achieved.

 

I would worry about timber laminate over ufh.

 

*Scottish rules sensibly require a bedroom on the ground floor. The rest is tiled.

[saveasteading]

1 hour ago, Gus Potter said:

 

@saveasteading has got a lot of info and knowledge about this so have a look at past posts. He also knows a lot about perimeter insulation

I guess so. Ask away.

[Gus Potter]

36 minutes ago, nod said:

If you are fixing matting to timber Use Ardex Absolutely Bombproof 

Ta @Nod thanks for the heads up, much appreciated.

[saveasteading]

3 hours ago, Sparrowhawk said:

We like the slight springyness of a suspended timber floor underfoot

Why not decide what floor you want, then look up the manufacturers blurb re ufh. Then we can work on a solution.

[Gus Potter]

1 hour ago, Iceverge said:

Another (slightly hippy) idea is an adobe (earth) floor.

Like that. Of course if you go down that route then it leads to more.. can you do passive stack ventilation.. can you use the adobe floor to balance and control moisture levels. Can it be used for example in historic buildings? Take an old Church you want you renovate and turn into a house. To comply with building regs you need to stuff in loads of insulation thus often shift the dew point in the walls detrimentally. If you have a moisture sink in the floor can you use these properties? Clay can absorb a lot of moisture. Is the adobe more enviromentally friendly, the processing can be I understand, but not always, less energy intensive (embodied carbon) than say making cement.

 

 

 

1 hour ago, Iceverge said:

I gather from those who run low temp heating in low energy houses that you don't get a hot UFH under foot feeling either. Please write in with the answers subscribers ?

I totally get the idea of low temp floors and passive house.. I'm a big fan of PH.. also a practical designer.

 

As a designer of homes I think about making it a home.. it's not an office.  Imagine you are unwell or your kids are off colour, an old person to look after.. it's good to have the option to crank up the heating and sod the bills. I know myself, how much and how good it feels to walk on a floor that is hotter than the norm. Build in that redundancy.. it's a luxury at not a big cost. Also, when we get say a "beast from the east" it's bit embarassing if your house is cold when guests come? yes..  the passive house is great normally but you can borrow my fleece and sorry the food is a bit cold and the red is a bit below temperature, and the old folk just want to go home as your house is bloody freezing.

 

If you are a dog owner then you need to create cool spots in the floor for them.. I used to have a German Shephard and kept a couple of cool spots so the dog was not uncomfortable.. he was part of the family and we all shared the same space. These are the types of things you need to finesse to make it a home for all the family.

Putting my SE hat on.. bouncy concrete structural slabs are a no no. Saying that for normal domestic applications your starting point is to say can we get a 100mm thick slab to work with the UF pipe, where do we need movement joints and that also drives the zoning of the UF loops.. another good reason to get your SE in early.

 

Even with the best designed UF layout it is almost impossible to not get the odd hotter spot in the floor as the pipes cluster when nearing the manifolds. If you try and avoid it then there is no free lunch.. you probably need to compromise elsewhere in terms of floor layout.. you end up chasing the dream... the builder turns up and does something completely different!

 

1 hour ago, Iceverge said:

Time over again I would avoid a concrete floor. 150mm concrete plus 200mm EPS here. 

I take your point but they do work well if designed taking into account the anticipated floor finishes and the home owners expectations.  Ok for me to profess but when you are in the thick of it as a self builder easier said than done when you probably have much bigger issues to deal with.

[IanR]

2 hours ago, Iceverge said:

I gather from those who run low temp heating in low energy houses that you don't get a hot UFH under foot feeling either. Please write in with the answers subscribers ?  @joe90 @TerryE @IanR@JohnMo to name a few. 

 

100mm Reinforced Concrete floor with UFH, on 300mm EPS here.

 

With a low flow temp of 30° the floor doesn't feel overly warm (except by a manifold), but certainly not cold.

 

In the living areas I've got 4mm of poured resin directly on the RC slab and I'd describe it as comfortable. It's a nice surface to walk on in bare feet. 

 

In bedrooms I've got low tog underlay under carpet on the same RC slab and also find this comfortable and warm. No issues heating the rooms, but I have a low heat demand.

 

In bathrooms I've got Porcelain tiles over the same RC slab with Ditra may. Floor feels slightly warmer than the poured resin, and dries really quick after a shower. 

 

Next house will have the same floor build up. 

 

35 minutes ago, Gus Potter said:

yes..  the passive house is great normally but you can borrow my fleece and sorry the food is a bit cold and the red is a bit below temperature, and the old folk just want to go home as your house is bloody freezing.

 

If I've understood you correctly, I think you have the wrong idea about a house built to passive house principles. For me it doesn't matter what the temp is outside, the temp inside remains stable. There's only been a couple of occurrences in 5 years, when I've been experimenting with turning the heating off for long periods, that the internal temp has dipped below 20.5°C

Edited April 25, 2023 by IanR

[JohnMo]

9 hours ago, Iceverge said:

gather from those who run low temp heating in low energy houses that you don't get a hot UFH under foot feeling either. Please write in with the answers subscribers ?  @joe90 @TerryE @IanR@JohnMo to name a few. 

 

@ProDave

 

@JohnMo has recently put UFH over insulation below 2 x layers of OSB floating. I am very interested in this approach. No wet trades. No crucifying hammering of your joints.   

Floor in main house 300mm centers on UFH, 200mm PIR and 100mm concrete screed.  Measured on a cold day, 30 deg flow temp, floor surface temp was 22, room just under 20. Floor never feels hot underfoot, you never actually notice it.

 

Our summer house floor is somewhat different buildup.

 

150mm EPS 70, 50mm thick UFH EPS moulds to give 115mm centres generally for the UFH. At 400mm centres above the EPS 70 there are 70mm wide wooden bearer. The whole lot is capped with 9mm OSB screwed to the bearers and a 50mm perimeter batten. A second layer of 9mm OSB is glued first layer (offset joint lines) and screwed through to the bearers/battens.

 

Not got the UFH operational yet, but floor has a solid feel, and no comments from the wife, which is a good sign.

[nod]

11 hours ago, Gus Potter said:

Ta @Nod thanks for the heads up, much appreciated.

👍

[Iceverge]

11 hours ago, Gus Potter said:

Can it be used for example in historic buildings? Take an old Church you want you renovate and turn into a house. To comply with building regs you need to stuff in loads of insulation thus often shift the dew point in the walls detrimentally

 

The maths suggest the only way deal with this is insulating the walls. EWI- as much as you like. IWI- breathable and probably better with a limited amount. Box in a box with a ventilated gap. 

 

11 hours ago, Gus Potter said:

If you have a moisture sink in the floor can you use these properties? Clay can absorb a lot of moisture. Is the adobe more enviromentally friendly, the processing can be I understand, but not always, less energy intensive (embodied carbon) than say making cement.

 

I don't know of any official figures about moisture regulation from natural materials, clay, lime, woodfiber, straw etc but those selling it do suggest so. I'd like to see some data. In its simplest form Adobe, is dug on site, screened and relaid. Very little embodied carbon vs concrete where almost all the CO2 is in the cement process. 

 

11 hours ago, Gus Potter said:

As a designer of homes I think about making it a home.. it's not an office.  Imagine you are unwell or your kids are off colour, an old person to look after.. it's good to have the option to crank up the heating and sod the bills. I know myself, how much and how good it feels to walk on a floor that is hotter than the norm. Build in that redundancy.. it's a luxury at not a big cost. Also, when we get say a "beast from the east" it's bit embarassing if your house is cold when guests come? yes..  the passive house is great normally but you can borrow my fleece and sorry the food is a bit cold and the red is a bit below temperature, and the old folk just want to go home as your house is bloody freezing.

 

The passive house and Passivhaus brigade are a bit evangelical at times.

 

"NO OPENING WINDOWS. 100% HERMITICALLY SEALED, SCI-FI AIRLOCKED EXTERNAL DOORS. NO AUXILIARY HEATING INPUT BEYOND THE MINIMUM AS DIRECTED BY THE COMPUTER PROGAMME"

 

I can hear the chants, I can see the placards. 

 

However in the real world it means that you don't HAVE to install central heating, but you need something. We have an electric rad. You don't have to comply with the dictated 20deg, you can ( and we do) have 23 deg in the sitting room for evening TV. You don't have to open the windows and doors for fresh air, but yet if the weather is nice we do, as the small kids transport contents of the house to the garden and the contents of the garden to the house.

 

The beast from the EAST is easily dealt with as the heating load rises to probably 2kw from 1.5kw. 500w is much easier to find than 20 or 30kw for leaky old pile.  In a powercut last year in the snow the house was still at 20deg upstairs and 19deg downstairs after 24hrs without power. Passive beats active every time. Guests are the best heaters of all, any party of above about 10 leads to windows being opened despite 9deg and grey, windy and wet outside. 

 

12 hours ago, Gus Potter said:

If you are a dog owner then you need to create cool spots in the floor for them.. I used to have a German Shephard and kept a couple of cool spots so the dog was not uncomfortable.. he was part of the family and we all shared the same space. These are the types of things you need to finesse to make it a home for all the family.

 

The dog lives in the hayshed thank you very much. Bringing the mutt inside is only one step away from putting him in a tutu carrying him around in a handbag. Cruel emasculation of a noble beast. 

 

12 hours ago, Gus Potter said:

Putting my SE hat on.. bouncy concrete structural slabs are a no no.

 

Why, why is nothing allowed to move and flex?!  Airplane wings bounce around for 18hrs per day for 40 years so it can't be the engineering. Is it a rigid mindset? 

 

12 hours ago, Gus Potter said:

Saying that for normal domestic applications your starting point is to say can we get a 100mm thick slab to work with the UF pipe, where do we need movement joints and that also drives the zoning of the UF loops.. another good reason to get your SE in early.

 

Even with the best designed UF layout it is almost impossible to not get the odd hotter spot in the floor as the pipes cluster when nearing the manifolds. If you try and avoid it then there is no free lunch.. you probably need to compromise elsewhere in terms of floor layout.. you end up chasing the dream... the builder turns up and does something completely different!

 

A super low flow temperature might solve this? Mind you, as you loose the warm floor feeling then i wonder what is the point of UFH at all then. 

 

11 hours ago, IanR said:

In the living areas I've got 4mm of poured resin directly on the RC slab and I'd describe it as comfortable. It's a nice surface to walk on in bare feet. 

 

This intrigues me. Is it a dear option? 

 

4 hours ago, JohnMo said:

screwed to the bearers and a 50mm perimeter batten

 

Was this necessary? Would it not have just floated ok? 

 

 

 

 

[JohnMo]

1 hour ago, Iceverge said:

Was this necessary? Would it not have just floated ok?

I didn't want to hit UFH pipes, or have screws hanging below the bottom surface and over time scratching away the pipe. The screws would be less than 18mm long if I didn't screw to battens.  Was a risk aversion based strategy

[Iceverge]

Gottya. Looking forward to hear how the UFH performs 

[IanR]

2 hours ago, Iceverge said:

This intrigues me. Is it a dear option? 

 

Not at 2017 prices, but it's gone up a fair bit now I understand. Equivalent to premium floor finishes, but not ridiculous. I paid £75/m², I believe now it's in the £100/m² to £120/m² range

 

 

[saveasteading]

5 hours ago, Iceverge said:

, why is nothing allowed to move and flex?

It is allowed to flex but it is limited for occupier comfort and confidence.

So a roof is allowed to flex to 1/180 of span, but a floor only to 1/360 from memory. Eg a 3.6m floor is allowed to bounce 10mm.

If it moves more than that, people get scared.

Elements are basically calculated twice. At what load it will fail. Then check deflection, and usually stiffen it up for that.

This applies to concrete as well as timber and steel.

[Sparrowhawk]

23 hours ago, Gus Potter said:

Good for you and good thoughts!

 

I have been doing up my own ex council house. I added an extension, laid some hard core, insulation, DPM and then a 100 mm thick concrete slab with A142 anticrack mesh... yes it is still the structural slab. I tied the wet UF heating pipes to the mesh. Then laid a layer of I think about 3.0 mm thick foam and floated a good quality engineered flooring over the top. I wanted a floating floor as opposed to glueing it to the concrete so I can lift parts if it ever get damaged, say by water or me doing something daft.

 

100% floating floors. I've lifted 2 floating laminate floors here to get to pipes underneath and it's made life easy. Helps they didn't tuck these ones under the skirting boards - which IMO looks poor but is easy to work with. I like the concept of 3mm foam as the underlay.

 

23 hours ago, Gus Potter said:

In another part I had the old timber suspended floor. Existing joist depth is 150mm. What I did was to get 50 x 50 timbers and fix to them 100 - 120mm wide rippings of OSB with plenty glue. The solum space is tight so then put plenty glue on top of the 50 x 50 (OSB on the bottom side) pilot drilled the joist at an angle and cheek screwed the 50 x 50 from above to pull it up hard against the underside of the joists, leaving a 150 mm ventilation space under. I had to do it this way as there is not enough room below the joists to a battery drill in to screw from underneath.

 

Now I had a 200 mm effective depth of joist with a ledge of OSB protruding. I then cut lengths of OSB nearly the width of the space between the joists and dropped them in so they rested on the OSB ledge. Next I cut 150mm PIR and fitted it tightly in between the joists. I went round any gaps with foam and then use silicont to really seal between the insualtion and the joists.

 

I need to lift a few more floorboards and check the level is consistent throughout to see if we've got anything like that depth. The knot hole I measured through gave 300mm from top of joist to earth. Fingers crossed I measured on a pile of crap and we have 350-400mm elsewhere.

 

23 hours ago, Gus Potter said:

Fixed to the insulation was the UF pipes, then a pug mix then the chipboardd flooring.

 

How much has this raised the floor by? Or are the UF pipes recessed between the joists, using the 30mm left by OSB+150mm PIR?

 

22 hours ago, Iceverge said:

Time over again I would avoid a concrete floor. 150mm concrete plus 200mm EPS here.

 

What would you go for next time?

 

22 hours ago, saveasteading said:

We've just fitted carpet on ufh.*

Special underlay has a large proportion of gaps. Then the carpet must also be open textured.

For laminate I don't know how this can be achieved.

 

I would worry about timber laminate over ufh.

 

Thanks and yes I've seen the concerns about timber laminate in other threads, plus the max temperature you're meant to use under it (which doesn't seem that high).

 

21 hours ago, saveasteading said:

Why not decide what floor you want, then look up the manufacturers blurb re ufh. Then we can work on a solution.

 

🤣 That decision is beyond us at the moment. Both through being indecisive people and because everything is at an early stage. I know OH's wish would be for some kind of herringbone in the lounge, and I'd like something more reflective (tiles?) in the dark, north-facing back of house. She's put off tiles because the ones we've got - upstairs in the bathroom laid on uninsulated chipboard, or in the kitchen laid onto concrete with probably 50mm EPS in the slab if we're lucky, are freezing cold!

 

UFH isn't decided - the first architect(ural designer - an interior designer it turns out) we had a free consultation with was all about knocking out a wall with 40% of our downstairs radiators against it to open it up, making a big space with nowhere obvious to re-site them. I like the idea of UFH to regain wall space to hang art and be able to position furniture but we will have to weight it up - and then do the thermal calcs. We'll be speaking to more architects.

[Iceverge]

2 hours ago, Sparrowhawk said:

What would you go for next time?

 

At least 300mm EPS. More is more as they say!! 

 

Maybe 2x layers of floating OSB over the top. Or a suspended timber floor with I joists and blown cellulose. 

 

 

[Gus Potter]

On 26/04/2023 at 00:32, IanR said:

If I've understood you correctly, I think you have the wrong idea about a house built to passive house principles.

Err no. I understand the principles... and the challenges you face integrating that with structural design. But also, understand the need to recognise how you need to balance that with how people live from day to day and what makes a home a home.

 

 

[Jilly]

Just now, Jilly said:

On 25/04/2023 at 23:08, saveasteading said:

I guess so. Ask away.

How much edge insulation can you use? I’ve noticed a potential cold bridge at the floor/wall junction. There is cavity insulation, plus external wall insulation (PIR) under cladding. We will get about 125mm of PIR (no more room but using Kooltherm K3 which is meant to be better than normal PIR) and then 70mm screed and ufh pipes. 

[saveasteading]

As a minimum there is the blue roll of foam that keeps the screed away from the wall and lets it shrink with minimal cracking.

I  would try to add PIR vertically to this, or only use PIR. The thickness depends on how much the wall will cover (and physically protect) it. Stud,service void, plasterboard, skirting.. Chances are you will have lots of off-cuts you can use.

 

It needs a detailed, scaled cross-section through the wall to floor interface to work this out.

Then draw arrows to represent the easiest route for heat to move, and try to improve it.

 

It is my opinion/feeling that there isn't a huge amount of heat loss through this junction, because the screed is thin and so the actual heat loss is not huge, with the insulation in the way. So getting 50mm in there is a big deal.

 

Of course it is more significant with UFH as the screed is at 30C or so.

 

Not enough is made of the area of the floor slab, ie distance to the cold outside. The ground is a good insulator.  So a narrow building will lose more heat to the ground than a wide one. In theory you could put lots of insulation depth near the outside walls and less near the centre. In fact you can use none in a very large space.

[IanR]

2 hours ago, Gus Potter said:

Err no. I understand the principles... and the challenges you face integrating that with structural design. But also, understand the need to recognise how you need to balance that with how people live from day to day and what makes a home a home.

 

What is it about Passivhaus principles that you feel run contrary to how people live day to day? and is that somehow related to your notion that that a PH home would be unable to maintain a comfortable temperature during a harsh weather event, such as "the beast from the east"?

 

Passivhaus defines targets for energy efficiency but isn't prescriptive on the capacity of the heating system.