Headlap working with reclaimed slates

[bazmdiy]

Hi all - please can anyone help me with slating low pitch roof with reclaimed slates?

I want to slate a 21 degree roof with a 450x225 (18"x9") slate. I've increased the headlap to 125mm (5") from about 80mm - but I'm sort of worried that this may not be enough. I'm reholing the slates 150mm from the top. The original holes are 175mm from the top. I attach 2 images of the courses and I'm particularly worried about capillary action around the red triangle.

Also does any one know if I can fill a hole to save a slate and whether there is a mastic to glue the odd slate where nailing would be awkward (eg cutting to finish a course on a hip)?

Many thanks

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[datarebal]

Your slightly under 125mm headlap at 165.. gauge.

How big are the original nail holes?
what is the slate quality?

Seeing as you have considered mastic, you might get away with using soakers on every slate then no need for mastic, glue , silicon..

obviously if its a big roof... cost could mount up

 

[bazmdiy]

hi datarebal and thanks for reply.

Roof is 62 sq metres (1800 ish slates?) so soakers could be tricky!

The slates are excellent but the old holes are on average about 10mm.

On the drawings the blue dots are the old holes and the green dots are the reholing. They are 25mm apart.

Its a single storey extension in Herts and we are in a sheltered dip in the land.

Its the capillary plume I'm a little worried about - and the fact that some websites say no slates below 30degrees!

I based my slate purchase and roof design based on the attached table of headlaps.

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ps I loose laid 6 courses and spayed with hosepipe. Left for 20 mins and removed slates. Two slates had plumes that threatened to enter old hole - otherwise all good. Not scientific but gives me a bit of hope! I also have a feeling that when nailed the slates wont touch so much and that might just do it.

 

[bazmdiy]

hi datarebal,

Sorry forgot to reply to your comment about headlap being less than 125mm. If the slates were 450mm then you are right - the headlap would be 120mm. However the slates are 18" x 9" which is 457.2 x 228.6 so the headlap is a bit better at 125mm.

 

[datarebal]

yes 125 headlap on a 457.2 slate.. of course I am correct on a 450mm slate.
Soakers not tricky at all and could solve the issue, remember bonds as important as headlap

capillary action has nothing to do with being in a dip.

 

[bazmdiy]

Hi - thanks for replying.

I attach image of roof. I wouldn't know how to apply soakers except at ridges. And they will be covered by lead flashing.

I will get the bonding within 2mm - its absolutely painstaking work since some slates are pretty irregular and over wide. I really got done by the seller and will have 30-50% wastage because many have been used twice and reholed inwards.

I am a born natural worrier and as usual I guess I'm exaggerating the problems here! I wish I'd seen the other headlap tables that said no 18x9 slates under 30 degrees.

One option I still have is to increase the headlap but to it would have to be massive to clear the old holes.

Do roofers ever have this problem and do they use mastic?

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[datarebal]

Firstly, you need to add another batten each side of your hip rafter from top to bottom. This will allow you to nail fix any cut slate. Correctly done there will be no need to stick anything.
Mastic is not the answer imho.. little more than a band aid.

i'd go with my soaker idea correctly placed will work a treat.
email me if you get stuck.

 

[bazmdiy]

hi again - do you mean soakers at the hip rafters only? I realise now that I should have left the hip rafters more proud but I can still use your batten idea..