Fitting new lean to roof under existing gable end roof line.

[john0wingnut]

Evening,

 

Looking for some help with a slight conundrum I have.

 

Below is a view of the side of my house, showing the existing conservatory, with lean to, hipped roof.

 

 

I am removing the polycarbonate roof and glass, retaining the dwarf walls and foundations.

 

New timber frame walls and roof will then be going on. Below is the SE's roof design thus far. T3s surround the rooflites. H1 are hips. T2 are headers over the doors / windows.

SE has specified roof timbers in 200 x 50, as span across the room is 3.4m. Jack rafters are max 1 meter span

 

 

Now the issue at hand is the space between the new timberframe head plate, and the existing gable wall undercloak board is limited. The current conservatory window / door frames are 2100mm high, top frame is about 80 mm, then roof is about 60mm, so total height is 2240mm. There is then a 35mm gap and then 165mm barge board.

 

 

Ive done a rough sketch below showing the new timber frame against the gable wall, with the top of the top plate siting at 2400mm. This leaves about 120mm to play with for rafters and roof covering, which doesnt currently work, given the SE wants 200mm rafters.

 

Gable End Detail.pdf

 

My only solution at present is to reduce the top plate height to 2350mm and change the rafters to 150mm. Im pretty sure the jack rafters could be 150mm, given minimal span, but haven't asked the SE yet.

 

If anyone has got any other ideas / thoughts, I am all ears.

 

John

 

[markc]

Instead on sitting rafters on top of wall plate you could notch them over the wall plate and support the lower edge with hangers onto wall plate. This would reduce your height while keeping the full depth rafter

[Temp]

Think it might look odd if the roof pitches don't match like they do now.

 

Presumably the problem goes away if the width is made a bit smaller? How much would you need to lose on the width to solve both issues? 

[john0wingnut]

On 27/01/2024 at 11:00, Temp said:

Think it might look odd if the roof pitches don't match like they do now.

 

Presumably the problem goes away if the width is made a bit smaller? How much would you need to lose on the width to solve both issues? 

 

The width has in theory been reduced, as the 150mm timber frame will be sat on the inner block leaf (all be it there is a query re that being allowable due to blocks only being 100mm and thus a 50mm overhang into the cavity), where as windows are currently sat on the outer leaf.

 

One thing I have now come across is a "Dutch Gable" where one essentially extends the existing roof at the base, then form a hip part way up. This I think will solve my problem

 

 

[john0wingnut]

Well, I spoke too soon.

 

Transpires that the original house, 1970s build, has an extra brick course on the left side vs the right. Im not even sure how that happens, given bricks are done in lines.

 

So I have 2560mm from DPC to undercloak board on the left, and 2440mm on the right, which makes the above plan impossible now, as the fascia boards will never align.

 

So I think my only option now is to lower the wall plate to 2350mm, then mount rafters on hangers on inside to allow enough space to fit a new tiled roof under the current one.