sprockets and roof "kick"

[RogerM]

I was intrigued to read about the subject of sprockets and the "kick" that they give to the lower roof slope in Colin's excellent shed build thread. , and was wondering whether this is this something that would suit a more conventional approach? I have just started a project for a shed with a New England style "saltbox" roof which will be covered with cedar shingles. The original plan calls for a simple rafter as in the top sketch below, but could it perhaps be amended as shown in the lower sketch to provide a "kick" to the first 3 courses of shingles? Again, the plan calls for a simple fascia and soffit attached to the end and underside of the rafter, so would installing a "kick" require a different approach to the way the ends of the rafters are treated?

Rafters are in 75 x 50mm tanalised and the shed will be clad in shiplap. The trusses are already built but not yet installed so if there are going to be any changes they need to be done now.

This is a picture of what I've been trying to emulate, but also like the idea of a kick to the lower roof slope provided that it enhances the overall lines. If it doesn't, I might as well just build it as shown.

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[MikeG.]

Roger,

providing a kick to that roof is the easy bit. It would IMO enhance the look of the roof quite a lot.

However, to do it the way you propose and box in the eaves is not an English look, nor a particularly attractive look in my view. Boxed in eaves are best left on housing estates.

In general terms, all (non-sheet) roof coverings with the exception of slates are suitable for use with sprockets. Clay plain tiles look the best, but almost any roof is improved with a kick to the lower course.

For your proposed building, I would advocate sprockets exposed in the normal way, with a simple eaves-closer at the wall line. Gutters can still be fitted, using rafter-foot brackets rather than face-fixed brackets. the detail is sketched here:

https://www.ukworkshop.co.uk/forums/viewtopic.php?t=24724&postdays=0&postorder=asc&start=30

Simple replace the beam in the drawing with the top of your wall.

Mike

 

[thejhw]

Mike, do sprockets increase the roof area?
I have a barn conversion and new garage both under construction at the mo' and really fancy the look of this.
Will the planners want to be told?

Jim

 

[MikeG.]

Jim,

the roof area is unaffected.

It would be a really picky Planning dept. that raised any objections to the use of sprockets after giving planning permission without sprockets. If you have exposed rafter feet on the original drawing I wouldn't have thought that there would be any problem at all unless you were in a National Park or in the curtlage of a Listed Building. Even then, I am sure they would welcome the change once the paperwork had been sorted out.

Mike

 

[EddieJ]

To add to what Mile has already said, I use sprockets quite frequently on the roofs my oak framing projects. In my case, I use them on frames where a full hip detail is shown leading to an aisle that has a different roof pitch. The sprockets take the degree of the lower pitch. I also always use sprockets if a warm roof has been specified. I will also use sprockets where a change from thatch to tile is being made on an existing building.
They are also a good way of slowing water down if the roof has a very steep pitch.

Unless specified, I don't tend to use sprockets on gable ended frames. The reason, is simply because it is another cost to factor into what is already an extremely competitive market. It's quicker and easier just to cut rafter feet and secure gutter brackets to either a fascia board or directly to the rafter feet. I know that Mike is a fan of the metal brackets, but from my experience, unless you get decent quality ones, they can cause problems later on.

 

[RogerM]

Thank you both for your comments.

Eddie - can you clarify what you mean by "rafter feet"? Are these just rafter ends that have a wedge above them to provide the "kick" and with the underside trimmed down to take the chunky square appearance away so that they don't have to be boxed in with fascias and soffits? Given that I have already built roof trusses as shown it would be nice to be able to modify these rather than have to rebuild them. The roof slope is 40 degrees.

This is for me rather than someone else paying a bill, so a bit of extra time isn't an issue. However, significant additional expense would be an issue and I'd rather not have to cut 20 sprockets in oak if I can help it. Something like this maybe?

How long should the sprocket be? How deep (top to bottom) at its maximum depth? I'm suggesting using 75 x 50mm tanalised because I have some in and it will match the rafters. Based on my drawing, it would appear that the depth needs to be greater than shown to provide a noticable "kick".

Or should I cut the rafter off along the line of the inside of the cladding and just have a sprocket beyond the cladding? This would imply a longer sprocket than shown in my drawing.

I will of course overhang the shingles beyond the sprocket by more than shown - I just ran out of paper! I have 2 inches beyond the batten planned.

 

[MikeG.]

Sorry Roger......deeper and longer than that.........further up the roof I mean.

Mike

 

[johnf]

Hi all

If you cut the sprockets with a vertical face to the end say 75mm deep you can screw standard gutter brackets to them doing away with the metal side brackets which are a pain to fix and you still create a kick in the roof which improves the overall apearance

PS most sprockets would be around 600 or 700mm long

 

[RogerM]

Sorry Roger......deeper and longer than that.........further up the roof I mean.

Mike

Thanks Mike. What became apparant when I drew it is that to give a kick to (say) the first 3 courses, the sprocket needs to extend well above that. So using 16" shingles with 5" exposed, does that mean I would have to make a sprocket 2 x 5" plus 16" - so 26" long? Would kicking the first 3 courses be about right?

 

[MikeG.]

Sorry Roger, as you can tell from my last post I was in a real rush.

Generally, sprockets are two-thirds on the roof, and one third off. Furthermore, generally the rafter line (top edge of the rafter), would spring from the top outside edge of a beam, or of the outer skin of the wall. You can run the boarding up as you have shown, but a nicer detail is to have an eaves closer board (a noggin, really), at right angles to the underside of the rafter (in other words, sloping out).

You can put a vertical face on an exposed rafter foot or a sprocket, and plant a reduced fascia board on that........indeed, I have that detail on my garage. however, every time I have done that I have regretted it afterwards. The hour or two of work that saves is at the cost of years of looking at it thinking "that isn't right, a traditional sprocket would have been better".

Mike