Thermal Expansion Cracking of Raft Foundation and Wall; A Passive House Floor Heating problem?

[Christian]

Is there anyone who can help me with information about thermal expansion cracking of the slab or walls in a passive house?

 

 

I have a technical concern regarding passive raft foundation and (ICF) concrete walls for a passive basement construction (part of a passive dwelling).

 

In technical terms:

Any solution to accommodate anticipated differential movement between the raft foundation concrete with an underfloor heating system and the concrete walls that sits on the raft foundation?

 

 

My concern is regarding the thermal expansion of the concrete in a raft foundation with an underfloor heating system.

 

 

The temperature of the concrete in the passive raft foundation may fluctuate with 8°C / 15°F or more, compared to the temperature of the ICF concrete basement wall, depending on the season and the heat from the underfloor heating system.

 

With the size of the raft foundation plat, this will induce a calculated expansion of the foundation slab concrete with 2-3 mm.

 

The ICF concrete walls, supported by the foundation system, does not expand, as the temperature do not fluctuate similar.

 

 

Perhaps we should made expansion joints between the raft foundation plate and the ICF wall, allowing them to slide the anticipated 2-3 mm on each other?

 

However, to make the basement construction strong, we would want to connect the raft foundation system concrete and the ICF concrete wall with reinforced steel.

 

Have anyone heard of this problem and any solution or guidance on how to solve it? 

 

Are there any experience about this potential problem anywhere?

 

Expansion cracks in a concrete slab can potentially damage technical installations in the slab, including the heating pipes in the floor/foundation plate.

 

I would very much appreciate any tips / advice. :-)

Edited October 16, 2019 by Christian
typo

[Jeremy Harris]

Welcome.

 

We have a passive raft foundation, with underfloor heating pipes cast into it.  Thermal expansion is tiny, as the temperature changes are also tiny.  When our heating is running flat out, in very cold weather (-10°C), the floor will be a bit over 23°C, for a room temperature of 21°C.

 

In very hot weather, we cool the floor, using the UFH pipes, with the ASHP working in reverse.  Typically the floor may cool to about 18°C in very hot weather. 

 

That's a tiny temperature change, just 5°C between the absolute coldest the slab gets and the hottest.  Parts of the slab get used to get much hotter just from the sun shining on them in summer, until we fitted solar reflective film on some windows to stop the house getting too hot.  I measured parts of the floor at ~30°C at that time, but there's no indication of any thermal movement.

 

Our slab is 100mm thick, and includes steel reinforcement mesh to strengthen it, and give something to fix the pipes to. 

 

I've worked in all-concrete buildings, with a concrete roof, that have experienced very much greater temperature swings than a floor slab will ever see.  The concrete roof of a hardened shelter would reach maybe 40°C in very hot weather in summer, and drop well below freezing in winter, yet I never saw any sign of cracking from this.

[Bitpipe]

I built a passive basement - 300mm reinforced steel / waterproof concrete (Sika).

 

External dims are 11500mm x 10500mm and internal wall height is 2700mm.

 

Slab sits on 300mm eps 200 and we dressed the exterior with 200mm eps 70.

 

We decided against any ufh in the basement slab and it works fine - always a comfortable 20 ish degrees down there summer or winter.

 

Standard dot & dab pb on interior, Jae dean on floor.

 

the basement is an ‘open box’  with a steel web over the top to support a suspended timber floor. This has wet ufh in Alu spreader plates under a 18mm osb deck. On top of that is 12&9mm ply and then a resin floor system.

 

MBC passive house on top which ties into the insulated layer of the basement.

 

So, I wouldn’t bother putting ufh in your basement, you will never need it.

 

[Bitpipe]

Just to add, I was wary of ICF for the basement walls as you can’t see the quality of the pour, compared to traditional shuttering.

 

While we’re well above the water table, the waterproof concrete is our only barrier so I wanted to ensure the pour was flawless. 
 

We used the warranties Sika system with water bars, mastic, plugs and waterproof concrete. It was all inspected and signed off by Sika to get the warranty.

[scottishjohn]

5 minutes ago, Bitpipe said:

Just to add, I was wary of ICF for the basement walls as you can’t see the quality of the pour, compared to traditional shuttering

you can,t see that till you remove the shuttering --and thats too late-

thats why you use a relativly  sloppy pour in ICF

and why you you vibrate it in a shuttered type with stiffer pour

 

[Bitpipe]

27 minutes ago, scottishjohn said:

you can,t see that till you remove the shuttering --and thats too late-

thats why you use a relativly  sloppy pour in ICF

and why you you vibrate it in a shuttered type with stiffer pour

 

While the concrete is green post shuttering strike you have the option to take it down if the pour was really bad - we never had to do this but there was peace of mind seeing the surface both sides.

 

We did cut into one green section of the stair enclosure outside the basement box and it was surprisingly easy to do but within a few days it was rock hard.