Wall plates different heights

[23vc]

Building my 2 storey side extension, and the existing house has a pier at the corner extending about a foot forward of the rest of the front elevation. I've built my extension 400mm back from this pier, as per the plans. However, to make the roof look right, ie. set back and dropped on the front face, I think I need to make my front wall plate lower than the back. I say this because if I set them both the same height, I end up with the front roof only about 50mm below the existing roofline, which I am worried will be in breach of planning and also a nightmare to flash down from the existing verge.
So - my thoughts are I can drop the front roof plane a bit (6 inches or so) by setting the front wallplate lower and have a small sloped section on the ceiling inside. Does this make any sense? I'm hoping I've not messed up in a big way as I didn't see this coming - it must be a pretty common thing though so hoping those more in the know may be able to comment?
I was still hoping to use trusses, but don't know if you can use a truss and set one wall plate lower by birdsmouthing it?
Cheers
John

 

[^woody^]

If a wall is set back then the plate would normally be higher not lower. Then the choice is ether -

• keep fascia in line with existing and same depth = wider soffit
• keep soffit level with existing and same width = deeper fascia
• keep fascia same depth and soffit same width = fascia and soffit at a higher level than existing

You need to measure down from the top of the existing rafters, as you need to allow for different rafter or truss depths above the plate. But the main thing is that the ceilings are kept level, so there is your datum line to work to, and the other dimensions fall into place naturally.

You would measure trusses from the existing ceiling joist height and the span between the two walls. Plate heights would be the same.

 

[23vc]

Thanks Woody. I am really struggling to explain this, what I'm trying to say is because of the existing house roof levels where the roofline crosses the wall, if I try and keep the new wall plates the same height it causes my new front roof to only drop by a couple of inches, so in order to force it to drop more I cant see any other option than to lower the front wall plate. I've tried to show the problem in the attached sketch (exaggerrated it a bit) side elevation view

 

[^woody^]

You have not set the front wall back enough to allow for a deeper roof drop.

The ceiling heights are the datum and this determines everything else naturally, based on where the levels and angles meet.

The only option for you now is to have a raised ceiling at the front and a section of sloping roof visible in the bedroom - a coombed ceiling

 

[23vc]

Thanks Woody, yes agree that I will need to have the sloping section visible. Thats what I'm trying to work out, that means I need the wall plate lower, is that right? Or is there some other way? I am trying to work out if I can still achieve this using standard trusses or whether I need to look at raised tie trusses or cut roof.

 

[^woody^]

But that will mean that your extension fascia is at a lower level than the existing, which will look worse than just having a smaller set down in the roof at the front

 

[^woody^]

With trusses, you will need to insert a beam at the point where the ceiling level meets the front roof slope, and the beam takes the place of the wall plate.

That will make the beam visible in the bedroom.

The alternative is the have a beam in the roof space, and a flush ceiling.

I might have a drawing somewhere for the alternative

 

[23vc]

re. the fascia, I understand where you're coming from but there is a massive overhang on the existing, so I think I will be able to match the height fine.
When you say beam am I looking at getting a steel up there? I was hoping it might be possible to just birdsmouth the trusses a bit further down below the tie? (or use raised tie truss with the b/mouths different height at each end?)

 

[^woody^]

Like this. The beam can be steel or timber

 

[23vc]

I've attached a better pic. The front wall is built set back *exactly* as per the plan.
However, what the plan doesn't show, is that the back roof intersection with wall is higher than the front. The back main house and extension wall actually run where I've drawn the black veritcal line just before the back wall.

Edit: Front of house is left on pic - back is right

This is because the front is actually a pillar so the roof has reached a lower point by the time it intersects with it. So, with the extension, I end up having to follow a similar layout, ie. lower at the front otherwise the front roof isn't set down enough.

Sorry this is a nighmare to explain and I'm really struggling to get my head round it - but really appreciate the advice!

 

[23vc]

Thanks for the pic - so the beam has a 2.8m clear span in my case - not sure what size I would get away with as its supporting the whole roof weight ? Is the wall then not taking any weight from the roof?

 

[Ian H]

Could you move it more into the room rather than lowering it? Might have to sit on a steel though.

 

[23vc]

Could you move it more into the room rather than lowering it? Might have to sit on a steel though.

I think that's pretty much what Woody's pic shows. I still can't believe I've got into this situation, its almost an optical illusion, I'm still trying to get my head round it. All I want is what's shown on the plan

 

[^woody^]

Have you got an image or the elevation view of the front elevation, plus the same for the opposite flank elevation to show the pier projection from the house

 

[23vc]

Front view and plan view attached if that helps? pier shown in both.