airtightness and electrical fixings

about2build

Sorry guys what would the importance of sealing up electrical conduits and sockets etc in a new build??? Trying to achieve a q50 of less than 1.5....i have been advised to use heat mastic to do the job.....any thoughts welcome?

Seal all the external walls and roof before first fix electrics if at all possible, then get all fixings on to internal structures wherever practicable to avoid punctures.

Outkast_IRE

I was in germany back in may looking at a whole range of passiv homes, the architects designing them were fond of a few things.

1. Smart desgin so alot of the sockets etc end up on internal walls, this helps everyone working on the job and helps a lot with airtightness.

2. When a socket was needed for sure on the interior of an external wall they liked to batton out one wall and have a mini service cavity inside the airtight layer, this service cavity would have a fill of rockwool or similar aswell.

3. They always aimed to have the airtightness work done, then do a blower door test and note the result. Only then leave the lads loose in the house doing their first fix work and make it perfectly clear that any accidental holes etc will show up when you do another blower door test at the end and if they are found to of caused the problem it will be taken out of their bill.

4. Understand that problem do occur if someone causes a hole in the airtight layer its a pain but its fixable the important thing is either to have someone supervising at all times or make sure the trades arent afraid to tell you if theres a problem.

Also important to note in this explanation is alot of archtects in germany are pretty hands on and often take on the role of construction manager/site foreman on their jobs.

sas

Outkast_IRE wrote: »

1. Smart desgin so alot of the sockets etc end up on internal walls, this helps everyone working on the job and helps a lot with airtightness.

This isn't necessarily the silver bullet it's described as. If you move the sockets for a corner on the internal wall, you still have to employ measures to airtighten them because air can move in the blocks themselves i.e. where the internal wall intersects the external wall, the air is free to move.

Outkast_IRE wrote: »

2. When a socket was needed for sure on the interior of an external wall they liked to batton out one wall and have a mini service cavity inside the airtight layer, this service cavity would have a fill of rockwool or similar aswell.

In my opinion and based on my own experience on our home, this is entirely unnecessary. Building a service cavity in a masonry build to accomadate cables is a huge waste of money.

What we did was to bed all socket backing boxes in with mortar i.e. they are not just nailed to bare block work. When the scratch coat was done the plasterers were instructed to really drive the scratch coat around any conduit and to ensure the backing boxes were again well bedded in.

We did our test at scratch coat stage. There were leaks at some sockets which I'm chalking down to the electricians not being 100% accurate when bedding the boxes into the wall.

We hit 0.32 with these measures, hence my confidence in my position.

Outkast_IRE wrote: »

3. They always aimed to have the airtightness work done, then do a blower door test and note the result. Only then leave the lads loose in the house doing their first fix work and make it perfectly clear that any accidental holes etc will show up when you do another blower door test at the end and if they are found to of caused the problem it will be taken out of their bill.

This is all well and good if you have tradesmen that will agree to that. I'd be of the opinion you'd be hard pressed here to be effective with that approach. Also, in theory it would work well for TF, I don't see how it would work in masony unless you are going to build service cavities everywhere. As stated above I don't agree with the need for service cavity in masonry build.

Outkast_IRE wrote: »

4. Understand that problem do occur if someone causes a hole in the airtight layer its a pain but its fixable the important thing is either to have someone supervising at all times or make sure the trades arent afraid to tell you if theres a problem.

The concern I have is when you have to complete certain details during construction with no way to test at that point but no way to recover if you get it wrong e.g. membrane wrap for hollowcore floor.

oldhead

sas wrote: »

This isn't necessarily the silver bullet it's described as. If you move the sockets for a corner on the internal wall, you still have to employ measures to airtighten them because air can move in the blocks themselves i.e. where the internal wall intersects the external wall, the air is free to move.



In my opinion and based on my own experience on our home, this is entirely unnecessary. Building a service cavity in a masonry build to accomadate cables is a huge waste of money.

What we did was to bed all socket backing boxes in with mortar i.e. they are not just nailed to bare block work. When the scratch coat was done the plasterers were instructed to really drive the scratch coat around any conduit and to ensure the backing boxes were again well bedded in.

We did our test at scratch coat stage. There were leaks at some sockets which I'm chalking down to the electricians not being 100% accurate when bedding the boxes into the wall.

We hit 0.32 with these measures, hence my confidence in my position.




This is all well and good if you have tradesmen that will agree to that. I'd be of the opinion you'd be hard pressed here to be effective with that approach. Also, in theory it would work well for TF, I don't see how it would work in masony unless you are going to build service cavities everywhere. As stated above I don't agree with the need for service cavity in masonry build.



The concern I have is when you have to complete certain details during construction with no way to test at that point but no way to recover if you get it wrong e.g. membrane wrap for hollowcore floor.

yea its a pain trying to seal around the boxes, my airtightness was after thought and just screwed the boxes onto the flat box as i was putting 50mm insulated slab around the electrical boxes. ended up sealing all the screws and holes in the boxes with Gripfill. it was an awful job