First floor clay block and beam heating slab

[passivhybrid]

We are building a poroton clay block 2 storey house ( with attic space liveable) to passive standards. Ground floor and first floor are 112 m2 with the attic space of circa 76m2. I bought the poroton clays directly from the manufacturer n Germany and went with their block and beam floor as well .

 

The block beam floor is essentially concrete reinforced girders with a poroton clay block 195mm high dropped in between the beams, then a 50mm concrete screed was poured. Having bookmarked @TerryE blog a long time ago , i now have the perfect opportunity to mimic his and others work albeit with a different cnstruction and on a different level to create a radiant ceramic slab

 

The only UFH i will have on the ground floor will be a circuit running around the perimeter of the building and another circuit for UFH panels which will be placed in the walls on the north elevation in living room and bathroom. In the attic space i dont envisage any heat being needed .

 

I have toyed with the idea of putting the UFH pipes on the ground floor ceiling and killing two birds with the one stone heating both upstairs and downstairs but electricians and others put me off. The poroton clay blocks in the floor will hold the heat for a long time so the UFH system i choose is variotherm which has the ability to be used as a cooling system as well. If i run with an air to water heat pump i will ensure it has a summer bypass function fitted still trying to figure out the Willis heater system

 

So having ruled out using the ceiling the Upstairs  floor will be used. Nearly 500 metres of piping is sitting in the garage awaiting installation but as of yet Nobody has being able to answere my queries on the need for insulation on top of the screed. The hollow clay poroton block is essentially 195mm of insulation on its own. If i put 75mm of insulation down on top of the 250mm screed and cover this with a screed of 75mm am I essentially blocking the heat going going to the ground floor ?. Giving that its a passive house and high decrement delay with the poroton the heat demand is not the primary deciding factor.

 

The variotherm rep forwarded my query on to their Head Office in Austria and that essentially there was no need insulation other than for a getting a fixing for the pipes but no need for fixing if i use their grid  underlay to hold the pipes in place . The only other point they raised was insulation might be necessary for sound as the blocks are hollow. Having walked on this floor screed for the last few months i dont think noise will be a problem.

 

What would you recommend? 

[PeterW]

2 hours ago, passivhybrid said:

The poroton clay blocks in the floor will hold the heat for a long time so the UFH system i choose is variotherm which has the ability to be used as a cooling system as well.

 

I take it the sales rep told you this and not the technical department ..?  Hollow clay blocks have a low heat capacity in comparison to a concrete block and beam floor. 

 

What is your wall build up as the Weinerberger site is very light on detail about uValues and to get Passiv levels you are going to need some insulation somewhere.

[A_L]

According to this site - https://www.bauen.lt/keraminis-blokas-wienerberger-porotherm-44-p-s the blocks have  thermal conductivity of 0.16W/m.K and thus a 440mm block would require at least 100mm PUR/PIR to reach the maximum Passivhaus U-value

 

Given the actual shape of the blocks do they have the same thermal conductivity in both horizontal directions?

 

[passivhybrid]

this is the wall build up, may add steico internal wood fibre on inside but dont think  i will need it, the €5k price for passive certification here is not worth it

[PeterW]

How is the Rockwool facade insulation attached to the porotherm blocks ..?? 

 

There is is no vapour control layers in any of that so the assumption is this is a “breathing” wall build up ..?? 

[passivhybrid]

42 minutes ago, A_L said:

According to this site - https://www.bauen.lt/keraminis-blokas-wienerberger-porotherm-44-p-s the blocks have  thermal conductivity of 0.16W/m.K and thus a 440mm block would require at least 100mm PUR/PIR to reach the maximum Passivhaus U-value

 

Given the actual shape of the blocks do they have the same thermal conductivity in both horizontal directions?

 

screen grab of manufacturers specs

 

I am not aiming to go the certification route for a passive house just following their criteria and using passive certified products for all the main purchases.

 

 

[passivhybrid]

yes its a breathable wall

 

airtightness is with a parge coat and in critical junctions blowerproof liquid ( which is also breathable)

 

rockwool to be attached with adhesive and insulation fixings

 

 

 

 

Edited September 24, 2019 by passivhybrid

[PeterW]

10 minutes ago, passivhybrid said:

blowerproof liquid ( which is also breathable)

 

How ......??? Blower proof by definition is a rubber type coating to stop air movement, which also prevents moisture moving through the wall. 

 

Assume this is HD rockwool batts that have been specified..??

 

Have you considered you could get a passiv(e) wall build up for 450mm using standard materials ..??

[passivhybrid]

clay block walls are already constructed we are at wall plate level now

 

i did consider conventional blocks but the breathability of the poroton block coupled with the heat storage capacity was why we went with it. 

 

we havent made a firm decision on the EWI as of yet will be next year before we need to make that decision, i have actually considered just pouring an external ringbeam around the perimeter of the Kore Passive Slab and just putting another skin of poroton up and blowing in cellulose in the newly created cavity, no fixings to worry about and simply lime render it job done  100% breathable. Finances as ever will dictate that dcision at the moment it looks like i will have 10 pallets of the blocks left. 

[passivhybrid]

33 minutes ago, PeterW said:

 

How ......??? Blower proof by definition is a rubber type coating to stop air movement, which also prevents moisture moving through the wall. 

 

Assume this is HD rockwool batts that have been specified..??

 

Have you considered you could get a passiv(e) wall build up for 450mm using standard materials ..??

https://www.blowerproof.co.uk/wp-content/uploads/2017/12/Blowerproof_Variable_Moisture_Control_Vapour_Control_Layer_VCL_Capacity.pdf

[PeterW]

32 minutes ago, passivhybrid said:

we havent made a firm decision on the EWI as of yet will be next year before we need to make that decision

 

Sorry for the daft question but how have you got this through building control ..?? If you’ve submitted a design based on EWI of rockwool, changing the EWI would need a change in submission. 

 

 

[Temp]

What's the u value for the ground floor? If the blocks are 0.16 and you have concrete beams bridging the blocks that layer will average worse than 0.16.

[Temp]

The screen shot above appears to say the thermal conductivity is 0.5 W/mk. If I remember correctly then to convert that to an approx u-value you divide by the thickness in metres. So if its 250mm thick the u-value is 0.5/0.25 = 2.

 

So unless I've made a mistake, which is quite possible, you definitely need insulation on the floors.

 

[TerryE]

IMO, certification is an irrelevance.  The core issue is thermal performance.  You need the correct mix of profiles to get your U-values and your thermal capacities right.  In your design the U-values are a bit high, I feel, and you don't have enough thermal capacity within the warm environment.

 

Block systems like this are common across the Mediterranean.  They have a lot of advantages, but they are nowhere near passive class. You would still need  200mm PUR in the walls to get this. Ditto under the block floor.  Look at the data sheets.

 

My floor profile has 300 mm EPS underneath the slab floor, and the slab floor beams have roughly 17 tonnes of concrete inside the warm environment.  The cellulosic filled twin-wall frame with outer stone skin only has a 0.12 U-value; the skin makes no material difference here, but it does dramatical improve the overall wall decrement delays.  All of this makes the room environment extremely stable. I only have about ±½°C daily ripple on a flat internal temperature set point yet only being heated overnight. 

 

This wouldn't be the case with a lower decrement delay profile and thermal capacity: you would need to heat throughout the day in colder periods.  There's nothing wrong in principle with a continuous control, except that using electric resistive heating on a flat or peak tariffs can get quite pricey. You would really need a high CoP rather than 1.0 such as a decent ASHP.

 

You need to start with a simple thermal budget calculator such as JSHs and plug in the numbers to make them balance before making finalising you profile and material selections. 

 

PS. On rereading this whole thread, I realise that this last advice comes too late. Maybe you can tweak the outer in insulation skin. You certainly need to think about correctly sizing your heating. / cooling system because whist  the house is better than min 2016 BReg standards, it isn't going to be passive-class.  The floor performance is a weakness, and you will probably need some upper floor heating for winter months, even if a few small 1KW oil filled heaters on timers.

Edited September 25, 2019 by TerryE

[passivhybrid]

11 hours ago, Temp said:

What's the u value for the ground floor? If the blocks are 0.16 and you have concrete beams bridging the blocks that layer will average worse than 0.16.

Thanks for replying and my Apologies for any confusion.The clay block and beam system is on the first floor i used it instead of a precast floor slabs at this level. 

 

the ground floor has u value below  0.10 it is the passive kore slab. in attached screen grab of ground floor  i have averaged out the  concrete because of deep ringbeam on perimeter of foundation plus horizontal and vertical ring beam inside slab

 

 

[passivhybrid]

12 hours ago, PeterW said:

 

Sorry for the daft question but how have you got this through building control ..?? If you’ve submitted a design based on EWI of rockwool, changing the EWI would need a change in submission. 

 

 

 Im not in the UK

 

My engineer is German and is quite familar with clay blocks and this system 

[Temp]

I've seen similar systems used by self builders in Belgium and thought they were interesting. Was it as easy to move the beams as it appears? I've seen photos showing a man lifting one end by hand but a lot of Belgian building sites seem to have mini cranes. How did it work out for you?

[TerryE]

Ah, the penny drops, and my confusion is explained.  The two photos in your original post are 1st floor profiles rather than ground floor.  Is this correct?   

 

I must admit I find it difficult to see what the advantages are for such a solid construction for internal floors within a single dwelling (though there are clear advantages for acoustic and fire separation in multi-occupancy dwellings).

 

We have a eco joist system for our upper floors and this really simplified the distribution of services, such as foul water and MVHR.  For example, it was pretty trivial to adopt a wet-room profile for all of our en-suites because we could trivially route our shower tray wastes within the floor void.   You must have quite a few layout challenges. ?

[Temp]

When we purchased a house in Belgium we discovered it had a solid first floor. No creaking when someone walks about. No problem with tiles in any room you like. Cool floors in summer. Liked it so much we built a beam and block first floor when we came back to the UK. In the end its a personal preference thing. Just as some people prefer brick and block walls while others are happy with stud walls.

 

The self build show in Brussels (called "Batibouw) had several companies promoting different ways to build solid floors. 

 

 

[passivhybrid]

On 25 September 2019 at 21:37, TerryE said:

Ah, the penny drops, and my confusion is explained.  The two photos in your original post are 1st floor profiles rather than ground floor.  Is this correct?   

 

I must admit I find it difficult to see what the advantages are for such a solid construction for internal floors within a single dwelling (though there are clear advantages for acoustic and fire separation in multi-occupancy dwellings).

 

We have a eco joist system for our upper floors and this really simplified the distribution of services, such as foul water and MVHR.  For example, it was pretty trivial to adopt a wet-room profile for all of our en-suites because we could trivially route our shower tray wastes within the floor void.   You must have quite a few layout challenges. ?

yes its first floor

 

I actually managed to route all the HRV ducts and first fix electrics within the 3 stiffening sections ( thinner blocks)and through the  hollow slots in the blocks. Used steel fibres in the concrete and increased depth of concrete by 50mm . Prior to concrete pour  I also drilled 100mm cores at each corner in building and in centre  to facilitate plumber and electrician.