parapet wall thermal bridging

[biryani_boy]

hi all,

quick question. we're finally ready to start building our extension, all the paperwork (covenants, planning permission, build over agreement, drawings) is ready. we already spoke to the builder and the project is straight forward.

the only "issue" is that we want to build parapet walls. this is because the neighbour is building an extension as well and since we get along, we both want to maximisie space, avoid awkward steps in the walls and gaps between external walls. the plan is to end up with something like this:

basically two parepet walls to continue the external walls of the house, brick/block onstruction, good insulation etc. I also want to build muy roof ("flat" roof, warm construction) between the walls. all well, but I've remembered discussions around thermal bridging with damp stains on the ceiling.

I've heard that you can replace the upper inner parapet wall with a stud construction that you fill with insulation to basically create a continuous insulation barrier between inside and outside. does anyone have any more information about this? diagrams would be helpful.

alternatively, some other options I can look at. also, I won't be able to have cavity trays, will I? the water would drain on the neighbour's side of the wall...

thanks

 

[bristolben]

Pretty sure the SkillBuilder channel on YouTube had something recently on precisely this?

 

[^woody^]

I've heard that you can replace the upper inner parapet wall with a stud construction that you fill with insulation to basically create a continuous insulation barrier between inside and outside. does anyone have any more information about this? diagrams would be helpful.

No, because it's complete nonsense and unnecessary.

 

[bristolben]

 

[^woody^]

Is that that Bisby bloke who knows f'all about building?

I used to see his inane reviews in builder mags, reviewing a plumbing fitting or a pencil and suchlike.

 

[biryani_boy]

No, because it's complete nonsense and unnecessary.

Are you saying I should just build a parapet as per the latest regulation using quality materials and I’ll be fine?

 

[^woody^]

There are no thermal bridging or insulation issues with a traditionally constructed parapet.

It needs to be properly detailed and then properly constructed, and whilst that goes for all parts of the build generally, it's a bit more important for parapets to get right.

 

[RonnyRaygun]

Why can’t you and your neighbour both do the same roof and not have a parapet?

 

[biryani_boy]

Why can’t you and your neighbour both do the same roof and not have a parapet?

We’re building at different times and his house is offset at the back by about 2m, so the extensiona won’t be symmetrical.

 

[Swwils]

Parapets are a geometric feature that act abit like a cooling fin. (Like other corner, but parapet has an upstand).

Why not just simplify?

 

[biryani_boy]

Because if I simplify and go for a “normal roof”, I’ll lose space. To avoid my roof overhanging on the neighbour’s land or to avoid it dripping rain on his roof, a parapet wall is the only option. We’re not looking to make it too tall, maybe 2-3 rows of bricks above the roof and it will slope down with the roof.

I’ll post a diagram later today, it would be good to get some good prwctice advice.

 

[Swwils]

doesn't your builder already have drawings of the details?

 

[^woody^]

a parapet wall is the only option

Get a better designer then and increase your options by at least 400%

 

[biryani_boy]

is there another option if the following are a MUST:

* no gap between the two extensions
* no loss of space, not even 1 mm
* no encroaching either boundaries, not even by 1 mm
* both extension built at different times with slightly different heights/roof types

if there is, I'd like to hear about it. having said that, I do like the took of a well-designed parapet wall, I just want to get it done properly to avoid any problems with damp.

 

[^woody^]

Yes there are options..

It just depends on which end of the 'skill/knowledge' and maybe the 'price' scale your chosen designer is at.