Pitched roof - extension length

[MarkT745]

Hi all,

Currently getting plans drawn up for a full width rear extension. The plan is for a pitched roof.

We had originally planned to go out 4m however concerned about shallow pitch. We think going out 3.5m will be just OK to fit in what we would like, but 4m would be better.

The difference in pitch angle looks to be about 18.9° at 3.5m and 16.7° at 4m (based on a rise of 1.2m).

I'm aware our next door neighbour couldn't go out any further due to the roof tiles, but aware there have been developments with tiles since they had their extension.

Is there likely to be any real disadvantage with the shallower angle (other than potentially tile choice?).

Thanks

 

[^woody^]

You can tile at any pitch with suitably designed sarking. Lowest pitch with tiles is 12° with a redland tile.

 

[tony1851]

I don't think it's just down to the sarking. Manufacturers won't guarantee lower pitches than they quote regardless of what's underneath the tiles.
They are also concerned that a lower pitch tends to stop the tiles draining as quickly as they should, and therefore they will remain damp for longer, thus giving problems in the winter.
@op; if the upstairs window cill is an issue, you can form a lead-lined cut-out in the roof where it comes up under the cill.

 

[MarkT745]

Thanks @tony1851 yes I'd heard about the cut out option (and yes the upstairs windows are the problem). Window cill to ground is around 3.6m. Other than aesthetics are there any drawbacks to the cut out option (i.e. maintenance, leak risk etc?). I'd like to try and get the angle to 17.5° as this seems to open up a lot more tile choice. Will have Velux windows too so will want comfortably above 15° which I believe is the minimum.

 

[^woody^]

I don't think it's just down to the sarking. Manufacturers won't guarantee lower pitches than they quote regardless of what's underneath the tiles.
They are also concerned that a lower pitch tends to stop the tiles draining as quickly as they should, and therefore they will remain damp for longer, thus giving problems in the winter.
@op; if the upstairs window cill is an issue, you can form a lead-lined cut-out in the roof where it comes up under the cill.

The roof is designed with a sealed sarking, ie flat roof on a pitch, and then tiled.

 

[freddiemercurystwin]

Except for all the holes in it.

 

[^woody^]

Are you referring to the gaps in your knowledge?

 

[freddiemercurystwin]

The gaps in your head.

 

[catlad]

Redland regent or mendip are suitable for 15 degree's Velux are about to launch a new version of their pitched roof skylights down to 10 degree's.
I wouldn't recommend working the flashing around your window unless you can find someone competent to do the work.

 

[Notch7]

Why not do a tiled skirt and a flat top.

You are thinking this the wrong way - if you want to come out 4 metres, don't compromise on that but make the roof work for the extension size

 

[sxturbo]

My brother had similar issue,

So he went for cut outs round the window, but he also had a side extension and it all had to tie in.

He used one of these online architects, the builder/carpenter wasn't very keen on the plans as it made them think more and cost more in time, the end result though was well worth it, as he has gone full eaves height inside it makes the room, doing a compromise wouldn't have had the wow factor they wished for.

Likewise don't compromise on the length, that extra 50cm makes a surprising amount of difference when you fill the space up, so I would advise against compromising on this also.

It's a lot of money to spend and have to make compromises on so don't make the compromise, you'll always wonder what if, or if only..

 

[MarkT745]

Thanks all for the replies. Will go back to 4m and see if we can make things work with the roof. I think you are right about compromising, I'd become a bit fixated on the roof pitch as know next door had issues, but that was a few years ago now and the tiles probably weren't available then.