DIY Loft Dormer Build - Gable End Wall Help

[curly82]

Hello All,


I am after a bit of help and advice.


I am currently in the process of building a loft dormer in my end of terrace Victorian property. This is my second attempt at a loft dormer after successfully completing one in a previous property some years ago. However this one is turning out to be slightly trickier..


Before starting i consulted my local building control officer who advised it was not permissible to support the RSJ for the Ridge Beam in the chimney breast as i had planned to do. After some deliberation i decided to remove the chimney stack and breast from the gable end down to the floor level of the loft so i could rebuild the inner skin to support the RSJ, thus preserving some much needed room space that would have otherwise been taken up by steels supporting the ridge.


I have got to the point where i have carefully removed all of the chimney stack and breasts down to the floor of the loft leaving the outer skin of the gable end and the header bricks in place. I now need to rebuild the inner skin and have a few questions on a few things i am unsure of...


(I should add, i am a keen DIYer who likes to tackle most things, but brickwork is something i do not have much experience with. I am trying to work out if this is something i can do myself or need to get a brickie in for)


1. The Outer skin of the gable wall leans in slightly. (Using a level the top leans in 40mm from the bottom) There is no cavity between the outer and inner skins so if i rebuild the inner skin following the outer skin it will also lean in. Is this acceptable, especially if i am going to be supporting the ridge beam RSJ from the inner skin? I am thinking probably not?


2. As i will need to cap the chimneys off with Concrete Lintels before building the inner skin. I had an idea to use 140mm Wide Lintels and starting my new wall from the edge giving me 40mm to play with to enable me to keep the wall straight going up to the top of the ridge. This would give me a 40mm cavity at the bottom, obviously narrowing to 0 as the inner skin meets the outer. Is this feasible and more importantly allowable?



3. What would be the best way to tie the inner and outer skins in? Just by using the current header bricks and building around them and cutting bricks or blocks to fit in or by using wall ties? Photos Attached


4. Would you build in the inner skin back up using the existing bricks from the chimney stack or use Dense blocks? I was thinking Blocks would be easier if doing it myself.


5. Or is none of this appropriate and i would need to get the outside and inside skins of the gable end totally rebuilt?

 

[23vc]

I’ll leave it to others to comment on the brickwork approach but if that gable is now single skin might be worth making sure it’s restrained properly to the rafters just in case? Fair play for taking that on tho...

 

[Leofric]

Shouldn't you be consulting Building Control again about building regulations approval and structural engineer's input for the structural alterations you are carrying out

 

[noseall]

1. The Outer skin of the gable wall leans in slightly. (Using a level the top leans in 40mm from the bottom) There is no cavity between the outer and inner skins so if i rebuild the inner skin following the outer skin it will also lean in. Is this acceptable, especially if i am going to be supporting the ridge beam RSJ from the inner skin? I am thinking probably not?

If you use 100mm blocks, there is a chance that the slimmer new masonry will accommodate the levelling discrepancy, starting as far away from the bricks at the bottom, as you dare.

2. As i will need to cap the chimneys off with Concrete Lintels before building the inner skin. I had an idea to use 140mm Wide Lintels and starting my new wall from the edge giving me 40mm to play with to enable me to keep the wall straight going up to the top of the ridge. This would give me a 40mm cavity at the bottom, obviously narrowing to 0 as the inner skin meets the outer. Is this feasible and more importantly allowable?

You can sneak a wee bit by corbelling over slightly, though I would not risk too much over-sail on a gable. You are far better doing as I said above.

3. What would be the best way to tie the inner and outer skins in? Just by using the current header bricks and building around them and cutting bricks or blocks to fit in or by using wall ties? Photos Attached

Strength and size wise - the original bricks re-laid would have been better. However slimmer blocks will give you a better chance to upright but it will mean faffing around the headers. It is important you secure those header with adequate pointing. Add the odd fish-tail or frame tie where necessary. Also be sure to add the gable restraint straps before embarking on the masonry re-build.

3. What would be the best way to tie the inner and outer skins in? Just by using the current header bricks and building around them and cutting bricks or blocks to fit in or by using wall ties? Photos Attached

A combination of ties and headers. Some headers will be sacrificed and some will stay. It is important that you don't rattle that gable about too much. Under no circumstances take the weight OFF the roof, The gable will rock like a grebo.

4. Would you build in the inner skin back up using the existing bricks from the chimney stack or use Dense blocks? I was thinking Blocks would be easier if doing it myself.


5. Or is none of this appropriate and i would need to get the outside and inside skins of the gable end totally rebuilt?

As above.

​

 

[^woody^]

Use bricks, build it plumb, use the existing headers.

Strap it to three rafters and floor joists, three maybe four straps to the front and back.

 

[noseall]

build it plumb

The gable leans in? It could mean chopping the backs of the bricks that bear the steels. Do you not think a slimmer 100mm block would stand a better chance?
I agree that the original bricks would sit better though...

Strength and size wise - the original bricks re-laid would have been better

 

[^woody^]

The gable leans in? It could mean chopping the backs of the bricks that bear the steels. Do you not think a slimmer 100mm block would stand a better chance?
I agree that the original bricks would sit better though...

A few course oversailing.

 

[tony1851]

Are there no purlins in the roof? As well as supporting the rafters, they also help stabilize the gable wall to an extent.
Make sure you tie the wall back to the underside of the rafters, preferably with three straps down the sloping part, and to the flat
roof when the dormer is up.

 

[noseall]

Also be sure to add the gable restraint straps before embarking on the masonry re-build

And then...

Strap it to three rafters and floor joists, three maybe four straps to the front and back.

Finally....

Make sure you tie the wall back to the underside of the rafters, preferably with three straps down the sloping

Has the OP got the message? (titter)

 

[Leofric]

Has the OP got the message?

Has anybody got the message that structural alterations require building regulations approval

 

[curly82]

Thanks for the replies everyone. Much appreciated. I will make sure to use straps to tie it all in to the rafters.

Leofric... A structural Engineer has already been consulted who provided cacls for the steels and advised that the chimney could safely be removed. I have also submitted a building notice and will be getting the BCO round again once the beams are in and gable end has been rebuilt to get it the thumbs up. I was just after advice here to make sure i do everything correctly before i get the BCO back.

 

[tony1851]

IMO the SE was taking a slight risk there. Removing the chimney and the inner skin and leaving a half-brick gable wall un-restrained is not good practice.

 

[Leofric]

IMO the SE was taking a slight risk there. Removing the chimney and the inner skin and leaving a half-brick gable wall un-restrained is not good practice.

Yes I agree ,the SE should have given more information to the client curly82 on the structural work required to ensure everything was structurally stable.

 

[^woody^]

It's common that if you ask an SE to design something, he will work out what's to be done, but won't tell you how to do it.

If there is a Principle Contractor or Designer under CDM (required but uncommon for domestic work), then they should be asking for the method statements.

 

[Leofric]

It's common that if you ask an SE to design something, he will work out what's to be done, but won't tell you how to do it.

but the SE hasn't 'worked out what's to be done ' regarding the gable wall have they ,that's the point surely ? !