Please review my foundation/floor/wall junction detailing

[Temp]

I think that's to stop water running out of the screed rather than act as a DPC? I've seen plastic sheeting recommended to help water retention during the curing process.

[Temp]

Sorry if already mentioned but.. Are you building internal walls off the B&B floor or off the screed/concrete? 

 

If the screed is going in after the internal walls then where the screed meets at doorways you should form an expansion gap. This is less important for timber floors but essential with tiles/stone. The screed will most likely shrink slightly towards the centre of each room pulling apart/cracking at doorways. The crack won't be straight and can curve more into one room than the other. It can propagate through the tiles as we found out.

[A_L]

@Hilldes you can fix UFH pipe to clip/mount rails which use adhesive patches to fix to any slipsheet/DPM without piercing it.

 

https://underfloorparts.co.uk/product/underfloor-heating-clip-rail-track-1mtr-adhesive/

[Hilldes]

14 hours ago, A_L said:

@Hilldes you can fix UFH pipe to clip/mount rails which use adhesive patches to fix to any slipsheet/DPM without piercing it.

 

https://underfloorparts.co.uk/product/underfloor-heating-clip-rail-track-1mtr-adhesive/

Thank @A_L that might br just what I need!

[Hilldes]

14 hours ago, Temp said:

Sorry if already mentioned but.. Are you building internal walls off the B&B floor or off the screed/concrete? 

Good point @Temp The non load bearing internal walls will be built on top of  the concrete topping.
 

The load bearing internal walls will have a section of ring beam supporting them. That detailing is next on my list, current thinking is the concrete/marmox block courses would extend up to support these LB internal walls in the same way as the external walls, but open to suggestions. 
 

P.S. flooring will be timber.

[Hilldes]

I though I'd post an update - sharing some lessons now we have the substructure complete, especially for anyone considering an insulated beam and block floor.

 

To recap, this features an insulated beam and block floor from Milbank - make up from bottom (as specified in the BBA cert of the insulated floor system, which I believe is used by a number of concrete beam suppliers that offer an insulated beam infill option?

• Conventional pre-stressed concrete T beams with EPS insulation infill the full depth of the beam, 
• A 150mm EPS top sheet across the top of the beams. 
• Damp proof membrane
• Structural concrete topping to finished floor level (there is no conventional screed on top of the slab). 

Underneath all this are piles plus reinforced concrete ground beams. The foundation blockwork supports a timber frame structure with 140mm studs - and blockwork is 140mm wide to match the timber frame.

 

Lessons:

 

1 making the blockwork the right height upto DPC. From my detailing, the final course of blocks to DPC would need to be 175mm high (not standard 215mm high for blocks). So the plan was to cut down the blocks lengthways so they were 175mm high. I hired a masonry bench saw with a view to accurately cutting down a large number of blocks - one course is >70 Linear metres so > 140 blocks. After cutting a few blocks with the masonry saw I abandoned this due to the time to cut each block and the fact the sliding table on the saw had no fence and I could see no way to attach one, so could not get accurate repeatable cuts. In the end I located two sizes of coursing bricks/blocks to make up the required height: W140mmxH65mmxL215mm and W140xH100xL440. These blocks cost me best part of £1K mainly due to the latter only being available in Cornwall and had high shipping costs (via Jewson). 

 

 

2. Telescope vents (needed for any suspended floor) - make sure the brickies build as specced. I specced the vents to be in the side elevations of the house which ran parallel to the concrete floor beams. The brickies did not put them in because they said they normally go in the infill blocks at the ends of the floor beams - which is fine for a conventional B&B floor as they will vent below the inserted concrete blocks. However, this won't work so well with an insulated B&B floor where the insulation infills extend the whole depth of the T beams. Another problem with placing the vents here as the front/rear walls has dropped thresholds so there would be nowhere for the vents above finished ground level. I now need to cut in the vents in the side walls where I specced them to be.

 

3. Fixing UFH pipes in a concrete slab. It's not uncommon to bury UFH pipes in slabs, however most seem to attach them to the topside of steel reinforcing mesh. The BBA cert for our insulated floor system specified that the steel mesh should be at mid height in the slab and there must be min 75mm concrete above any "services". So our UFH pipes would need to go under the steel mesh. We opted for self adhesive clip tracks. They struck fine to the DPM. However when the pipes were clipped in they pulled the clip track upwards and the DPM with it - with such force that in places the pipes also lifted the steel mesh to the point it would have been protruding from the top of the slab. There was no option but to place some staples at the pipe loops to keep them down. I'm not sure what the alternative method of fixing the pipes would be, perhaps plastic pipe tray, but not sure how the chairs for the steel mesh would sit on these.

 

4. Ordering Readymix concrete. So my CAD model told me the slab had a volume of exactly 14m3 - which I'm sure is correct. So I ordered 14.2m3 - 0.2m3 for contingency as we don't want to be short when pouring a slab right? I also had not subtracted the volume of UFH pipes (almost 1km of 16mm pipe) and steel also in the slab which should mean we had even more ready mix left over. When it came to the pour we were indeed short of readymix and it was too late to order some more from the plant. By chance we had a bulk bag of aggregate, a mixer and many bags of cement, so we mixed some more conrete - all of the bulk bag and we were still short. We got the last couple of barrowfulls from our spoil pile where the pump had been emptied. Lesson is that you need to allow for vibrating which we did that allegedly gives a better finish and stronger concrete but reduces the volume of the concrete and also allow for the waste in the pump (substantial) and readymix truck. 

 

5. Generally very pleased with the insulated floor system - very easy to install and all quantities calculated correctly by manufacturer. Beware the insulation comes by default on an artic due to the sheer volume - we had to pay for the shipment back to warehouse then back to us on two smaller vehicles when the artic driver refused to enter our road.
 

Edited March 18, 2021 by Hilldes
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