Low pitch roof

[Antony Robinson]

Hello,

Need some advice on one storey mono low pitch roof. Details are.....

pitch = 12.5°
3 off 114cm x 118cm centre pivot velux windows (SK06)
Flash kit to be EDW for tile includes insulation & felt collar
Tile to be either redland regentm marley melodie of forticrete centurion

I know that velux are only guaranteed to 15° but due to other contraints I'm stick with 12.5°.

Main roof above it diverts rain elsewhere so there will only be approx 2m2 of area of tiles above each velux window. Home is in the east mids so weather not too extreme.

Also neighbour did the same 5 years ago and all is still watertight, although the windows were only 90cm.

Has anyone had experience of using velux at below recommended pitch?

Really do not want the FAKRO with increase angle flash kit as they look too industrial.

Ant

 

[garyo]

Has anyone had experience of using velux at below recommended pitch?

It's a chuck of the dice at that level. Peoples success seems be down to each individual situation and quality of fit, and it'll depend on how sheltered the roof is by other parts of your structure - i.e. have you built it facing away from the prevailing weather direction in your area, and is it built in to the corner of a larger 'L' shaped 2 storey house so that the wind 'stalls' rather than blowing a gale right over the top, under the tiles, etc.

If your neighbour has done it, and your roof is oriented the same way, then that's a good indicator. However, it might be that his roof tiles and Velux flashings are actually leaking like a sieve but the roofers applied a high attention to detail on the underlying membrane and it's that that's saving the day (for now) so make sure

 

[catlad]

In your case its 20 degree's minimum pitch with tiles
I would advise buying a storm collar and cross your fingers.

 

[Antony Robinson]

20 degrees? why?
Does anyone know what is better? redland regent or forticrete centurrion for 12.5 pitch.
Also struggling knowing where to put the trimmers for the velux windows. I was going to put then bang in the middle of the length of the rafter from inside but am concerned about getting it in the right place for the tiles.
I think the forticrete seems to work better than the regent for getting the right tile gauge without requiring cuts below the velux window.

 

[hardmetalking]

Zinc is the answer....

 

[Antony Robinson]

Well, I'm sure some of you guys will say I told you so but I'm going to take the risk at 12.5°. Spoke to about 4 local roofers who have all seen the roof and the location of the house and they seem to think that it should be OK.
I've bought redland regent smooth tiles & 3 keylite roof windows.
I'm amazed how difficult it is to just find some plain non opening roof windows but they all seem to be twice the price of the opening centre pivot ones.
Roofer has said that he will double felt around windows and also felt above the laths around windows, similar to a felt collar.
Roof windows come tomorrow so I'm going to look at the flashing kit and see if it's possible to actually raise the top edge by 45mm and still have it perform it's function. If not they will go in at 12.5°.
I'll try and ensure that the lower flashing area is done so to avoid any horizontal bits that may cause puddling.
I'd be amazed if velux offer a guarantee at 15° without a safety factor built in to the design.
Any, fingers crossed.

 

[catlad]

I saw one of the leading manufacturers has recently launched a new flashing kit a bit like you described with a raised top section, Fakro maybe?

 

[Antony Robinson]

I've only seen the fakro low pitch roof system, also advertised by forticrete but they raise it an additional 10 deg which looks awful. OK for a commercial building but not for my home.

 

[catlad]

I got a lot of calls over the last winter when it was raining
for days on end about leaking skylights
mostly what builders had installed thinking 15 degree's
is enough for a tiled roof when 20 degree's is the min.

 

[Antony Robinson]

why would 20 deg be the min when both velux & keylite guarantee at 15 deg?

 

[catlad]

I think you will find that with the flashing kit required
for those tiles the minimum pitch is 20 degree's

 

[Antony Robinson]

Halfway through doing the low pitch roof. Employed a roofer to complete the job over 3 days but unfortunately he walked out after I a few disagreements. Oh Well.
Anyway main roof is 12.5°. The tiles are redland regent with at least 100mm overlap so should be OK.
Also installing the keylite felt collars.
Now that the windows are in place I've been investigating how much I can increase the angle of the windows without affecting the function of the flashing (nearest window). This is what one of the roof window engineers said that I should try as well.
Tried to achieve 15° which required 50mm upstand at the back but after fitting the flashing & tiles there was too much distortion and was worried that I may break the flashing joints.
So had to compromise and only raise it 25mm with an extra batten. After some slight movement of some of the metalwork it looks like it will be OK when the tiles are installed.
Now the angle of the windows is approx 14°. Still under the 15° requirement by Keylite but at least is should help a bit.
Used a grinder on the tiles below the window to help the low flashing kit. Tested it with a pint of water. It runs off the metal tray OK but still get very small puddles where the corrugation joins with the metal plate.

20160803_200625[1]

• Antony Robinson
• 3 Aug 2016

Low Pitch Roof

 

[noseall]

What on gods gracious Earth is going on with the bottom course of tiles!

Whoever designed that roof at that pitch is an amateur.

 

[Antony Robinson]

Bottom course is OK. I've moved the tiles up temporarily to remove the eaves protectors that were put on wrong.
The roof never really got designed from scratch. Neighbour has the same size rear extension and his dwg stated 15°. I copied his drawings and kept the extension the same size to ensure 15° after learning about roof window limitations.
It wasn't until the bricky got up to wall plate level and we measured it that we realised we could only get 12.5°. After lots of measuring & re-measuring it still only came out at 12.5°.
Finally measured neighbours roof pitch and it came out at 12.5° also so it was wrong in the first place!

 

[noseall]

Keep your fingers crossed.

At least there will be a period of time to test the windows once they are in. However, it is wind driven rain that will be the main culprit so keep those fingers crossed.