Sarking Boards or increased headlap?

[hammerswinger]

Hi,
I'm constructing the roof on my ongoing single story extension on the back of my house.

The rafters are in place & have turned out to be at 19 degrees, this is due to window height. I believe that there's a difference between rafter pitch & tile pitch but I'm not sure how much this will change the pitch or if the tile specifications take this into account?

The tiles for the roof will be Marley Wessex that go down to a 15 degree pitch.

I'm wondering if it's a wise step to use sarking boards on the roof or would an increasing the headlap to 100mm be ok?

What do you think?

Thanks.

 

[DAZB]

Much cheaper just to increase the headlap and not much chance of leaking in because of the breather membrane also but the choice is yours really for your piece of mind or budget, which ever is the stronger.

 

[hammerswinger]

Hi,
I forgot to mention that the ceiling of the extension is going to be vaulted so there will be 100mm of between rafter and 50mm of under rafter insulation both kingspan type, the roof will also have 3 Velux windows in it if that makes any difference.

I initially thought of using sarking boards on the roof before it was built, I just thought they would make it a nice solid job, however using them adds more expense & a lot of work and I don't think the cost & effort justify it, so I think I'll go with increased headlap and save a lot of time and expense.


Thanks.

 

[hammerswinger]

Hi,
I've worked out the gauge of the tiles and I can either go with 8 rows of tiles which will give an approx headlap of 96mm, or I could have 9 rows which will give a 132mm headlap.

Can anyone see a problem with using a 132mm headlap?

The bigger headlap looks like it will work out better for the tiles above & below the Velux windows and as the roof is only a 17 degree pitch I thought it may be better.

I can go with either headlap but I thought I would ask what you guys thought?


Thanks.

 

[catlad]

I think an almost 4" headlap will be ok for your roof as it is relatively small. make sure to use felt support trays at the bottom of your roof to prevent ponding should any water get onto your breather membrane. you can get a roofing sitework guide from marley give them a call 01283 722588. also offer the first 3 or 4 rows single tiles in a line will do just to make sure they sit ok with the facia board.

 

[hammerswinger]

Hi,
Thanks for the reply.

Have decided to go for the 96mm headlap which I'm sure will be fine, I have the Eaves protectors (felt support trays) so will be using those along with maybe some comb filler.
I'm not sure if the comb filler is the best choice for the Wessex tiles as they have a big flat area so I would end up cutting most of the spikes off the comb strip and only leaving a few at the high parts of the tile, maybe there's a better filler available for the tile.

Thanks for the tip about the roofing site work guide, I found it on line, it's available here:

http://www.marleyeternit.co.uk/Resources/Sitework-Guide.aspx


Thanks.

 

[Alastairreid]

I'm not sure if the comb filler is the best choice for the Wessex tiles as they have a big flat area so I would end up cutting most of the spikes off the comb strip and only leaving a few at the high parts of the tile
Thanks.

The eave combs are flexible you dont need to cut them.

 

[hammerswinger]

Hi,
Yeah but if you look at the wessex tile it is only raised at the interlocking bit, so you have a large flat area, the comb spikes will be totally folded over along the flat part and the spikes of the comb will probably hold the tile up a little so it would probably be best to cut the spikes off along the flat area of the tile only leaving them where thy are needed.

Maybe there are individual fillers available for tiles like the wessex.


Cheers.