Wall Plate Question

[John Smith Esq.]

Hello,

We are having a house extension built, single storey with a hipped roof. The builder has built the inner skin block work up (fibolites I think) but found that there is an awkward height difference from the current top of the block work and the wall plate of the existing bungalow, which the roof must tie in to.

In order to make up the difference, he could cut 20 fibolite blocks in half and then use the 4x2 wall plate called for in the roof instructions. This would be a crap dusty job for him though. So he has suggested making up the difference by instead adding a course of concrete commons to the top of the blockwork and using 4x3 as the wall plate.

Does this seem reasonable? He says it will be stronger and better if anything. The only issue I can think of is extra weight. He says the building inspectors usually prefer the same material for the inner skin, mentioning a time when he used to do the corners of blockwork in brick. I assume that was to do with thermal values though (?) and this proposed top course is above the insulation anyway (above the outer skin).

I would be most grateful for any views on this.

Thank you
John

 

[noseall]

In order to make up the difference, he could cut 20 fibolite blocks in half and then use the 4x2 wall plate called for in the roof instructions. This would be a crap dusty job for him though. So he has suggested making up the difference by instead adding a course of concrete commons to the top of the blockwork and using 4x3 as the wall plate.

Concrete commons - no.

Fibolite coursing bricks (or similar density equivalent) - yes.

We use either, i.e. cut blocks or lightweight coursing bricks, depending what we have on site or what ever is most economical.

 

[Ricke21]

It's true about mixed materials but that's for a number of different reasons. Whatever the cut is it be worth doing it.

 

[John Smith Esq.]

So is the problem weight? But if the blockwork is able to hold up a roof, what difference would a single course of commons make?

If he uses the fibolite blockettes instead, which I think are the same size as a brick, is it OK for him to use the 4x3 plate rather than 4x2?

 

[John Smith Esq.]

It's true about mixed materials but that's for a number of different reasons. Whatever the cut is it be worth doing it.

What are these reasons out of interest? Just so I am armed with the best info when I talk it over with him.

 

[noseall]

So is the problem weight? But if the blockwork is able to hold up a roof, what difference would a single course of commons make?

If he uses the fibolite blockettes instead, which I think are the same size as a brick, is it OK for him to use the 4x3 plate rather than 4x2?

The thickness of the wall plate makes no difference. We use both depending on make-up. 4" x 3" tanolised is sold and specified as wall plate.

 

[noseall]

What are these reasons out of interest?

As long as the bricks are aerated, it makes no difference. Concrete commons - no.

 

[Ricke21]

What are these reasons out of interest? Just so I am armed with the best info when I talk it over with him.

Mainly u value and reaction. Not all material hold the same u value. Also some materials react different in different circumstances. So it could affect the integrity of the building. A lil over kill but something happened somewhere for these to be a raised issue. Not all building control will pick up on it

 

[John Smith Esq.]

As long as the bricks are aerated, it makes no difference. Concrete commons - no.

Why do they need to be aerated?

 

[noseall]

Why do they need to be aerated?

Or lightweight.

Same material as the blocks basically.

 

[John Smith Esq.]

Or lightweight.

Same material as the blocks basically.

But why would one course of commons matter when a whole roof will be sat on the same block work?

 

[noseall]

But why would one course of commons matter when a whole roof will be sat on the same block work?

Eh?

The issues are thermal, not weight.

 

[John Smith Esq.]

Eh?

The issues are thermal, not weight.

Right, but as I pointed out in my original post, the commons would be at the top of the blockwork, above the wall insulation. They would be at or above ceiling height.

So are commons fine after all?

 

[cdbe]

I could have cut 20 blocks in the time it took you to write this post.

 

[23vc]

So are commons fine after all?

As said, the risks are that the top course of that wall (ie top 3 inches of your internal wall below ceiling) will have slightly different (worse) thermal insulation, and may also have differential expansion/contraction compared to the section below it.

Whether or not that’ll ever manifest itself in a noticeable issue, no one can say.