Full fill cavity insulation beads

tobeme2020

Hi, I will be building my 30sqm, 1 large room and bathroom extension in the summer and have the option of full fill cavity boards or Kingspan pumped full fill beads.

After pricing the two, the beads are just over half price of the boards. I am going to get the walls pumped because budget is tight.

One question I have is after the beads are pumped, do they sit on the foundations or is there anything to keep them off it. I have concerns the insulation beads would get damp at this location and create damp patches in my new extension. The cavity will be 150mm.

sydthebeat

The insulation should extend 225mm below the floor level.

No need to go to the foundations, you should build the rising walls as solid masonry

tobeme2020

sydthebeat wrote: »

The insulation should extend 225mm below the floor level.

No need to go to the foundations, you should build the rising walls as solid masonry

If it's a raft foundation, isn't that 225 below floor level. The insulation beads will sit below this. This will be underground

sydthebeat

tobeme2020 wrote: »

If it's a raft foundation, isn't that 225 below floor level. The insulation beads will sit below this. This will be underground

There will always be more than 225 between the top of a standard raft foundation and the finished floor level..... Unless you're installing a completely insulation wrapped raft...

Can you sketch your detail please

bfclancy

won't the house have a tray dpc detail usually 225mm below either finished floor level or top row of footings

tobeme2020

sydthebeat wrote: »

There will always be more than 225 between the top of a standard raft foundation and the finished floor level..... Unless you're installing a completely insulation wrapped raft...

Can you sketch your detail please

IMG_20210522_080821.jpg



This!

You can see on the sketch, the insulation rests on the radon barrier and dpc that is on the toe of the raft but it's also underground. I can't help thinking below ground where the block meets the insulation, there will be damp penetrating through and up into floor level on the inside. My understanding this is whst the cavity was for so the board insulation wouldn't meet the exterior blocks. This can't be achieved with the pumped kingspan bead insulation.

muffler

Did you forget about the DPM?

tobeme2020

muffler wrote: »

Did you forget about the DPM?

, nó. The dpm will be under the insulation or if flow screed, above it. Even if the dpm is in, the insulation can get wet u drrgriund. Thsts a given and can start rising above the dpcs. Bad weather in winter at the bottom of the cavity will get wet.

BryanF

muffler is correct, additional dpc required at above outer first block

It would be better if the ground level was lower than the radon

tobeme2020

BryanF wrote: »

muffler is correct, additional dpc required at above outer first block

It would be better if the ground level was lower than the radon

Other rafts I've seen have always been underground and the ground level always above the dpc. Even if there was dpc above first block, the bottom beads can still get damp. The dpc on the first block will only stop the rising damp on the block, not the beads!

What I intend to do now is, 450mm high 150mm full fill xtratherm insulation at this detail. Cut in a slope from from the floor level to the first block and install a dpc on top continuous around the bottom of the building then full fill beads above this. This would be a better option IMHO.