Cold bridges in this design

[puntloos]

This is a provisional design, but are there any cold bridges in here? I understand there might be, but I can't see where.. anyone a bit of a passiv designer?

 

[Olf]

All the beam and block floor and wall junctions are. You can mitigate it with adding internal wall insulation (if going PB with service cavity route), the higher it reaches, the better  - and contributed to wall U value. Or make a thermal break at the slab perimeter insulation level with Thermoblock or alternatives. Depending whether you use UFH or radiators the rationale may change a bit - with rads these cold bridges are of less penalty, as the floor is relatively cold, with UFH they'll turn some of the effort of warming inside into heating the foundations instead (perimeter insulation helps, but only so much as 25-30mm can, and then unprotected wall sponges the heat and takes it to teh dungeon underneath).

Saying that, most people just move on and live with the standard detail as on your drawings. Calculating losses due to psi values is a bit more esoteric than U, so it is harder to get return on investment in extra insulation/thermal break calulation.

[puntloos]

There's a few other things that I'm missing:

 

Specifications for wall ties seem incorrect for low energy building
No thermal breaks on kitchen frame steel structure

 

Anything else that we should consider adding?

[AliG]

This is similar to the blockwork in my house and you can feel the floor is colder next to the block walls that go down to the foundations.

 

What I don't know is whether the cost of eliminating these bridges pays for itself.

 

The thing that more surprised me is the cavity internal walls. I have some thick supporting internal walls, but they are made from wider blocks (Porotherm). I would have thought the normal construction for these is blocks laid on their side, not a cavity.

 

I have one small area where there are two internal block walls with a cavity in between. No one thought to insulate this wall, but it connect through to the outside wall and is obviously colder than all the other walls in the house. It is also a problem for airtightness and the cavity is connected to the outside cavity.

 

It is also an enormous waste of space, you have some 400mm internal walls, why are these not solid 200mm walls?

 

Those doors sliding into the wall cavity are also an airtightness problem. You need to make sure the builders seal up the cavity behind the doors, which they won't do unless they are made to do it.

 

 

[Mr Punter]

Another vote for the Marmox Thermoblock installed at the same level as the floor insulation on the inner leaf of the perimeter walls.

[puntloos]

3 hours ago, Mr Punter said:

Another vote for the Marmox Thermoblock installed at the same level as the floor insulation on the inner leaf of the perimeter walls.

 

Ah this seems to make sense. 

5 hours ago, AliG said:

This is similar to the blockwork in my house and you can feel the floor is colder next to the block walls that go down to the foundations.

Don't... all ground floor block walls go down to the foundations? 

 

5 hours ago, AliG said:

What I don't know is whether the cost of eliminating these bridges pays for itself.

 

The thing that more surprised me is the cavity internal walls. I have some thick supporting internal walls, but they are made from wider blocks (Porotherm). I would have thought the normal construction for these is blocks laid on their side, not a cavity.

Do you have any drawings so I can understand what you mean?

 

5 hours ago, AliG said:

 

I have one small area where there are two internal block walls with a cavity in between. No one thought to insulate this wall, but it connect through to the outside wall and is obviously colder than all the other walls in the house. It is also a problem for airtightness and the cavity is connected to the outside cavity.

 

It is also an enormous waste of space, you have some 400mm internal walls, why are these not solid 200mm walls?

 

Oh, partially loadbearing, partially noise reasons. Home Cinema. 

 

5 hours ago, AliG said:

 

Those doors sliding into the wall cavity are also an airtightness problem. You need to make sure the builders seal up the cavity behind the doors, which they won't do unless they are made to do it.

I don't think they're supposed to slide all the way into the cavity wall indeed, but I'll make sure. What should be used to seal it up? Spittle mixed with wood shavings? 

 

[AliG]

48 minutes ago, puntloos said:

Don't... all ground floor block walls go down to the foundations? 

 

Usually. If you use a raft foundation they can just sit on the raft with EPS underneath it. I think though using the Marmox blocks as suggested as the way to reduce the cold bridge.

 

49 minutes ago, puntloos said:

Do you have any drawings so I can understand what you mean?

 

53 minutes ago, puntloos said:

Oh, partially loadbearing, partially noise reasons. Home Cinema. 

 

Couldn't find a drawing, but if needed to support a heavy structure upstairs you can simply lay blocks on their flat side, so you get a 215mm wide wall instead of 100mm(They can also lay them back to back which looks like how the wall between the hall and office is built). They did it in the extension of my last house so they could support concrete floor planks above. In your case though, it seems that you have a block cavity wall between the living room and office and around the utility area. Such a thick wall won't be needed structurally, it will be for sound deadening and the sliding doors and then to separate the utility area as it is being built like a garage.

 

If the builders are left to themselves they will leave the cavity of the wall between the office and living room open to the cavity in the external wall and there will be no insulation in the cavity. Thus cold air could come all the way from the external cavity right into the house via the sliding doors.

 

If you build the wall this way I would want the cavity closed to the outside cavity. I would probably put insulation in the cavity for all it costs and then I would close the cavity before at the point the sliding doors slide back to.

 

It does't really mater how it is sealed. Plaster/foam/tape etc. Just make sure that you don't have a draught blowing around the doors and cold air behind the uninsulated interior walls.

 

Personally I think I would have a single skin wall and then frame out an area to put the doors into. This would probably cut 100-150mm off the wall thickness. Noise reduction will come from better detailing. TBH with a door through the wall it will be very difficult to stop noise travelling.

 

The wall around the possible garage area is less of an issue as I guess they plan to insulate it and treat it like an outside wall. You could save 100mm by making it single skin and framed insulation or 200mm by making it single skin and PIR. But you would have to take into account fire regs.