Setting out roof.

[cdbe]

I'm building a small two storey extension at the front of my house. I need to extend the existing pitched roof.
I hope the photos are fairly self explanatory:

The plan is to extend the right hand face, I guess along the lines of that bit of facsia that's hanging off. The new tiles are flat interlocking (Marley modern style) with a minimum pitch of 17.5°. The existing rafters are 75mm as will be the new ones.
The distance from existing wall plate to new wall plate will be about 1.25m.

What I'm trying to work out is where to finish the new wall plate to achieve the required pitch - I'm assuming that's how you set it (top of wall plate to top of wall plate)? Is there a guide or formula, or is it worked out a completely different way?

On a general note, is it a good idea to go down to the minimum pitch? I know attention to detail is important, and things like making sure the runoff from the left of the valley goes to its own gutter etc but is there anything else?

I don't have a clue what the pitch of the existing roof is, but will I have a problem with the tiles where the pitch changes?

Any other suggestions appreciated, the aim is no leaks and maximum internal headroom.

And just to possibly complicate matters a bit further, that outer skin behind the slanting fascia is coming out.

Thanks.

 

[catlad]

Small warm rubber roof seems a lot easier.

 

[cdbe]

That's probably true, would it look a bit odd against the pitched roof? I just can't picture it.

 

[^woody^]

Are you saying that you are just throwing a roof on at some or other random pitch? Not matching the main roof?

If you go in the loft, you normally find rafters to get the pitch off

But TBH I'm only guessing at what I think you might be doing. Its not clear to me. Don't you have some sort of fag packet with a drawing on it?

 

[cdbe]

Are you saying that you are just throwing a roof on at some or other random pitch? Not matching the main roof?

Of course!

Trust me Woody, my drawings will just add to the confusion.

Hopefully this will make it clearer:

This is the same style of extension and main roof as mine:

I'm trying to avoid the flat roof if it's not too much extra effort (although having found a "real life" one it doesn't actually look that bad to me).

This is mine, narrower at the front but if I continue with the existing pitch it's going to cut out half the room inside:

If I can reduce the pitch it might work:

I think that a 17.5° pitch is about 1 in 3, so over 1.25m the height difference is 400mm? So does this just mean I set the new wall plate 400mm lower than the existing - check my sums and the tiles will be right?

Assuming so, I need to have a think about inside - this is what the slope looks like inside:

Will the room look stupid like that? It will be even lower with insulation under, about 1.95 at the wall rising to meet the existing at 2.4.

 

[^woody^]

I suspect a flat roof would look much better than a frankenroof.

Gables or hips don't seem to work, and would need a horizontal valley/gutter

So ... a cat-slide may help to take the eye off the flat roof and break up the brickwork

Or 18°, low ceiling and low window

 

[oldbutnotdead]

I suspect..... frankenroof.

What a fine word, I need to find a use for that

 

[noseall]

Gotta be a flattie there surely? But keep the fascia detail running level with the existing. You may have to conjure up some building gymnastics to avoid a deep fascia (dealing with the additional insulation thickness) but it is possible to look acceptable.

 

[cdbe]

Ok, getting closer now. Going for a warm flat roof.

The top of the joists will finish around the top of the bricks. Technically I think this means that I could run the fascia round at the same level (at the bottom) as the existing. The question is, should I do this at the same projection as the existing (200mm) or return it in and fix directly to the wall, or somewhere in between? I'm not worried about overhang as I think the reclaimed Accrington's will handle the splashes and rain, but I think the detail of the bottom hip tiles will be better if the flat roof is set back?

I'm also going to poach @noseall s genius idea of setting the insulation back to avoid the massive fascia height, so I don't know whether this affects how much or not I project the fascia to get the hip tile looking best?

Hopefully the pictures make things a bit clearer.

 

[freddiemercurystwin]

This is on the front elevation presumaby, so you would need planning permission for what you are doing.

 

[Koolpc]

Didnt you plan all this upfront?

 

[cdbe]

This is on the front elevation presumaby, so you would need planning permission for what you are doing.

I have planning permission, in conjunction with my large rear extension. I can't remember what vague drawing of that little bit of roof was submitted but the planning officer had absolutely no interest in the front.
Obviously from my point of view I want something that looks least odd - I don't think any warm flat roof sitting so high up does look natural but that's where I am. With hindsight, as I'm replacing the entire roof, I wish I'd just built out the valley or even gone hip to gable.

 

[freddiemercurystwin]

Are you saying your approved drawings don't show what type of roof was proposed at the front?

 

[cdbe]

Are you saying your approved drawings don't show what type of roof was proposed at the front?

Fill your boots:

Fully approved parapet squiggle detail.

 

[gonch69]

Should of extended ridge the width of extension put new hip in and infill to line of back roof would of lost that valley doing so too