Timber frame 1.5 storey with 1 storey extension - thermal bridge suggestions?

brophis

Hi,

Building a 1.5 storey timber frame house with a single storey section to the side as per picture attached. Have a wall coming up through the extension to join with the external wall to the outside of the extension. To my knowledge this is going to create a cold bridge from the ground up through the wall and into the room and from the external wall down into the room. I'm trying to come up with ideas to reduce the cold bridge.

A few thoughts I had so far were:

1) Add a course of low thermal conductivity blocks to the bottom of the wall and a course or two at ceiling level

2) Build the entire internal wall from low conductivity thermal blocks and rise to meet the external wall

3) Add a course of low thermal conductivity blocks to the bottom of the wall and put insulated plasterboard or a service cavity filled with wool/fibreglass type insulation inside the internal wall.

I'd be interested to hear your thoughts on the above or any other suggestions you might have. I'd also be interested in getting some suggestions by PM in relation to options for low thermal conductivity blocks. I'm only familiar with ones beginning with q.

Many thanks

brophis

Hate to bump my own thread but just wondering if anyone had any thoughts at all? Getting close to decision time.

homewardbound11

Hi,
I had the same issue and went with block. That section of the house is always a tad colder in the cold weather (even though insulated). I thought of cement board but how do you merge block to cement board if the rest of the house is in block and especially the plastering. Your idea of quinn lite blocks is a good alternative. Could you use steel lintel at eve level and raise your wall from that using block. I guess an engineer would be required for that.
Sorry, just thinking aloud from the same problem I had a few years back with my own home.

Eoghan Barra

Hi Brophis,

I am also building a 1.5 storey house with a single storey section projecting out to the front. Like Homewardbound11 though, I am using block.

I was faced with exactly the same problem as you describe and decided to have a 100mm high course of high density 300 EPS polystyrene built into the walls at joist level to reduce the thermal bridge. I used offcuts from the insulated foundation for this. The blockwork is also in thermal block (not quinnlite, alphatherm), which should also help lessen the cold bridge.

I have never seen this done before and am aware that it's somewhat unorthodox (blocklayer thinks I'm a nut), but my attitude is, if it works with no forseeable problems, why not. I was also reassured by the fact that the blocks are 140mm wide rather than 100mm.

I'm not very familiar with timber frame construction, and this may not be much help to you, but I suppose the message is if you reflect on the problem you'll find a solution even if you have to invent one yourself.

brophis

That's a novel solution Eoghan. Did you have normal concrete blocks above the EPS?

Eoghan Barra

brophis wrote: »

That's a novel solution Eoghan. Did you have normal concrete blocks above the EPS?

No, I used alphatherm lightweight blocks both above and below the EPS in both situations, but that was as much for structural reasons as for helping to reduce the thermal bridge.

In the first instance, where the single storey structure meets the 1.5 storey, an internal dividing wall becomes the outer leaf of the 1.5 storey section. There is no extra reinforcement in the concrete floor slab underneath, so I wanted the wall to be in lightweight blocks from the bottom to the top to reduce the load. The internal wall underneath the EPS is of 140mm alphatherm, while above that it is of 100mm alphatherm, married in at each end with 100mm standards. This is the only area in the entire building where lightweight blocks were used in the outer leaf, everywhere else they're 100mm standards.

The second instance is in the inner leaf at the gable end of the single storey projection. All of the inner leaf blocks (as well as internal walls) in the entire building are alphatherm 140mm, so here they continue above and below the EPS.

The course of EPS is at joist level because cellulose insulation will be used between and above the joists in the single storey structure.

brophis

Do you notice the difference to touch? Are the standard blocks much colder?

Eoghan Barra

The house is still under construction, but once occupied - and heated - the alphatherm should be warmer to the touch than a standard block inner leaf.