Rear extension floor build up

[HughF]

We're looking at putting a single story rear extension under PD on our end of terrace which currently has suspended timber floors downstairs. My neighbour and friend, who is a builder, is going to do the work for us as I'm too busy with my day job and am a bit rubbish with a trowel and my wife wants standard masonry construction (I'm at home with sticks and a nail gun).

 

Same neighbour put their rear extension on with a concrete slab floor, concreting over their air bricks. 

 

1. Do I need to worry about concreting over my air bricks? My gut says yes. I'm not sure if the ventilation carries through to the front of the house, or whether the dwarf wall in the middle of the house is solid. There are air bricks at the front of the house too.

2. I want UFH in the extension, should I consider beam and block to retain an under-floor ventilation void?

3. The downstairs room which will open up into the extension needs some floor repairs and insulation, but I don't want to rip it all out and cast a new concrete floor in situ.

 

Thoughts?

[Temp]

I'd go beam and block if the cost is ok. If you block the vents that could encourage rot in the existing floor. It's also easier to do ufh and or tiles if you have screed floor.

 

Just check the floor levels work out as b&b, insulation and screed are quite deep.

Edited April 6, 2022 by Temp

[TonyT]

Don’t block the air bricks, they are required to keep your existing timber floor in good condition.

 

ducts can be installed to extend the airflow to the new out walls in the extension

[HughF]

7 minutes ago, TonyT said:

Don’t block the air bricks, they are required to keep your existing timber floor in good condition.

 

ducts can be installed to extend the airflow to the new out walls in the extension

Agreed, blocking the air vents seems like a disaster waiting to happen. I'd rather go for solid floor than beam and block (probably easier for this small space), just got to sort the ducting out I guess.

[JohnMo]

If you are going for UFH make sure the floor is well insulated.  Aim for a U value of 0.15 or better.  Circa 200mm PIR will give around 0.1 or 150mm around 0.15.

 

Screed on top of the insulation and UFH pipes to bring the floors level with existing.

[jayc89]

3 minutes ago, JohnMo said:

If you are going for UFH make sure the floor is well insulated.  Aim for a U value of 0.15 or better.  Circa 200mm PIR will give around 0.1 or 150mm around 0.15.

 

Screed on top of the insulation and UFH pipes to bring the floors level with existing.

 

Doesn't that depend on your P/A ratio? For me, with a PA Ratio of 0.4, 100mm PIR resulted in a u-value of 0.15

[JohnMo]

20 minutes ago, jayc89 said:

 

Doesn't that depend on your P/A ratio? For me, with a PA Ratio of 0.4, 100mm PIR resulted in a u-value of 0.15

True, based on 0.4 P/A.

 

100mm is 0.14

150mm is 0.1

[HughF]

I was going to go for pipe-in-self-leveller 50mm buildup at 120mm spacing. I wanted something with moderate-fast thermal response, to match the overlay system I was going to add in the rest of the down stairs, and to appease the wife with her demands for a responsive heating system (although I'm hoping that when we get the UFH working on an ASHP, I can just set and forget the room stat)

 

Hoping that I can get the floor build up level enough that I can just bang the self leveller down onto 200mm of PIR and be done with it.