No cavity masonry walls in Scotland???

[saveasteading]

We are told by a local builder that cavity walls are not done in Scotland. (Perhaps 'up here' just means in the area)

We have a section of stone wall to replace, and had drawn a cavity block wall onto which would go external cladding.

 

Drawing of breath...you can have that if you want but it isn't how we do it, and it would be expensive.

 

So they propose a single skin, thick block, structural wall. Small gap then stud and insulation inside, the same as we are gong to do to the stone walls, and clad outside as planned.

 

To my mind this is not cheaper, slightly less strong,  and loses the benefit of the insulated, water resisting, cavity. 

But I am open to their advice and we don't want to have them learning new techniques on our money.

 

Any comments to confirm or deny this is the local way.?

[Gus Potter]

In fairness to the builder they may have a point just not communicated the concept very well. Also, they may not have a full grasp of all of the issues such as continuity of the insulation envelope and so on.

 

"We have a section of stone wall to replace, and had drawn a cavity block wall onto which would go external cladding."

 

The first question is how big is the section? A few metres or a lot? and how does it interface with the existing stone walls? If it's a short section then I would look to see if there is any merit in rebuilding it in natural recycled stone from the site to match the existing using the same mix of mortar (or as close as you can). Here you can mitigate the effects of shrinkage and avoid the difficulty of trying to bond a cavity wall to a solid stone wall.. this can be time consuming to get right. if the existing walls are a bit loose then you find you keep having to remove more and more until you can make a good bond (tooth) between the new and existing...

 

If you use concrete blocks then they do move about differently from any existing stone walls. It may be that you can take this approach and move the external "rain screen" to another location if it intended to be a feature?

 

"So they propose a single skin, thick block, structural wall. Small gap then stud and insulation inside, the same as we are gong to do to the stone walls, and clad outside as planned." 

 

How thick is the single skin to be? 100mm, 215mm (block on the flat) or more?

 

"Any comments to confirm or deny this is the local way.?"

 

It might be for small infill areas but these days we tend not to go for solid wall construction as a first option, unless it is retaining something or is on say an onerous fire boundary.

 

 

[ProDave]

Scotland has been set in the ways of timber frame for decades.  So TF is "how we do things up here"

 

But that does not mean it is the ONLY way, it means anything else most builders will consider "unusual"

 

I can't see a problem with lack of bricklayers, after all if they can find them for the outer skin why not the inner.  Perhaps they don't trust BCO to pass it and don't want grief, but again up here you need a building warrant which is akin to "full plans approval" in England.  So if it's on the plans and BCO have approved the plans and it is built to the plans, BCO will pass it.

 

I know of a pair of new houses built in Lairg a few years ago that are built entirely of cavity brick and block with no TF involved, because that is what the (English) customer insisted on.

[saveasteading]

Thanks. As I thought. I am open minded about it. 

 

We are not rebuilding in stone, although there is plenty in the wall to use again. But the local masons are in short supply and doing well with patching and pointing. We wouldn't get a gang for a year, and then it would be expensive.

Aesthetically a modern face will work well in this rear position. Planning have given a blank slate, so we could build it in log cabin, pyramid, or Taj mahal style if we wanted.

 

We are keeping the main facades (3/4 of it) old and 1/4 will be new with timber cladding and metal roof. The timber will be stained to keep the fresh colour permanently.

 

Structurally, the area is pretty well a whole wing, and junctions will be at corners and  it wont cause undue stress. Even with lime the block wall will move less than the rubble, which joggles to suit. But we will match the footing depth, and allow 'soft toothing' my new term for......not sure quite what yet...perhaps a construction joint with cladding over it.