Deciding on eaves height for single storey extension

[sambotc]

I am in the middle of plans for a single storey extension to the rear of my terrace house, permitted development.

One part I am struggling to decide on is the eaves to the new rear wall, which will have a window and a French door in.

The rear of the existing house has a fairly low window in, so I am limited to the roof pitch angle of the new extension (lean to arrangement) so I am trying to plan for the eaves height of the new wall to be as low as possible.

With that in mind, from finished internal floor level, the new French door is approximately 2000mm high? and the ceiling height in the existing house is approximately 2300mm. I also need a lintel over the French door obviously so I need to allow for that?

Does anybody have any guidance or links I can use to plan out the eaves height, wall height and lintels etc?

Much appreciated

Sam

 

[tony1851]

The patio doors may be nearer to 2.1m high. If the doors are not too wide, a two-course high lintel should be OK, then a 50 or 75mm deep wall plate on top of that. Your pitch should be no less than 15° if you are installing rooflights.
If this still comes over the cill of the window, you can do a small lead-lined cut-out in the roof just below the cill.

 

[sambotc]

Thanks Tony. I've been looking further into it and see that you can buy metal eaves lintels which are angled to reduce the outer block work by a course or so?

Are these OK or would you avoid?

 

[noseall]

Thanks Tony. I've been looking further into it and see that you can buy metal eaves lintels which are angled to reduce the outer block work by a course or so?

Are these OK or would you avoid?

Are you on about a stubby eaves lintel. If so, these are designed with ease of fitting the soffit board etc and are to do with the non-relevant outer leaf. The upstand and inner leaf masonry, which will be doing all the work, the height of which will be determined by the span of the French doors. It is likely to be a two or three course lintel.
We often omit an outer leaf lintel when the soffit detail means that the soffit board is resting on the masonry.

 

[sambotc]

Hi Noseall,

Not quite sure what you mean, sorry!

This was the sort of thing I had in mind?

 

[noseall]

The upstand is sloped towards the outer leaf in order to facilitate water run off when dealing with interstitial condensation and the use of cavity trays etc. It's also a handy when dealing with roof pitch - agreed. But all cavity lintel upstands have some degree of slope towards the outer leaf.

However, the lintel in your image is indeed an eaves lintel showing a much shorter (stubby) outer leaf flange and is to allow the soffit uninterrupted passage into the widow reveal. As I said, we often just use a box lintel on the inner leaf, in this situation, omitting any outer leaf support completely.

The issue of lintel upstand height still remains in that a greater opening span could mean a deeper lintel upstand and no amount of lintel upstand slope is going to change that. You need to factor in a 2.1m door height + lintel upstand + wall plate + rafter depth etc when considering eaves height.

That said, the slopey bit on the lintel upstand may be a boon when deciding on a nice deep birdsmouth cut in that you will avoid striking the upstand due to its shape. We have had to do a second notch on the rafter in the past when a steel beam has been used over window opening. So - yes, the upstand shape may gain you a few more mm.

Presumably we are talking a cut roof and not (lean-to) mono trusses, as to the roof design?