Help! Badly slated new roof?

[Knottypinehell]

Hello!
I'm new to the forum so please forgive possible topic duplication.

I recently contracted a local roofer (via checkatrade - got 3 quotes) to strip, felt and slate my 1930's bungalow which previously had french clay interlocking tiles leaking all over the place.

I opted for natural slate as it is lightweight and looks much better than concrete tiles.

The roofer has almost finished (after being delayed by the awful weather) so today I went up onto the scaffold to inspect the work. Unfortunately the results are frankly shocking. The house is over 85 years old and I appreciate that the roof structure isn't going to be true and flat. However, the newly slated roof is humped and dipped in various places and the majority of the slates do not sit flat, kick up (by more than an inch) and some slates are already broken, chipped and don't butt up laterally (pictured below)

Am I wrong in thinking a competent roofer is able to compensate for uneven substrate with proper measurement and workmanship (to a certain degree)? Isn't the roofer supposed to sort the slates prior to slating? Isn't the roofer supposed to adjust the battens to compensate for unevenness?

The slates around the velux are kicked up so much I think they would be ripped off by a strong gust of wind. I'm really at a loss as to what to do, because I'm pretty sure he will say its because of the 'old roof' structure and there's nothing he can do (although he didn't mention it would be a problem before). As you can imagine this isn't a cheap job and I don't want to pay the balance until I am satisfied.

I would be really grateful for anyone's opinion as this is really stressing me out.

Thanks in advance for your thoughts.

 

[catlad]

He does not know what he is doing, and that is not the correct flashing kit for the window.

 

[noseall]

I'm pretty sure even the best roofer would have a job bending large slates to suit that awful roof.
Poor choice of tiles.
The roof timbers should have been attended to prior to fitting something as unforgiving as large slates.

 

[catlad]

Correct Noseall but thats knowing your job.

 

[Knottypinehell]

Correct Noseall but thats knowing your job.

Correct - why would a roofer give a quote for slates vs tiles if slates are so unforgiving? I'm not the expert - he is. Never was it mentioned that this problem would occur.

Can anything be done?

 

[noseall]

Correct Noseall but thats knowing your job.

Correct - why would a roofer give a quote for slates vs tiles if slates are so unforgiving? I'm not the expert - he is. Never was it mentioned that this problem would occur.

I opted for natural slate as it is lightweight and looks much better than concrete tiles.

 

[gregers]

lets hope we dont have any more strong winds.
im not a roofer but looking at that i can see future problems.

 

[Knottypinehell]

Correct Noseall but thats knowing your job.

Correct - why would a roofer give a quote for slates vs tiles if slates are so unforgiving? I'm not the expert - he is. Never was it mentioned that this problem would occur.

I opted for natural slate as it is lightweight and looks much better than concrete tiles.

I was given option of slate. I am not a roofer.

 

[noseall]

I was given option of slate. I am not a roofer.

And YOU chose slates yes?

 

[tony1851]

The roof will sag here and there over time because timber is subject to long-term creep under load, but that would not explain the individual slates sticking up here and there.
When a slate sticks up, it can be because the nails in the slate below have not been driven down flush with the batten. To me this suggests poor workmanship rather than a serious problem with the roof structure.

 

[palaceray]

The worst issue is the area around the Velux. As a minimum this area should be stripped off and a proper slate flashing kit installed and area reslated.

The slates seem to be Spanish and Spanish slates are often twisted and do not lay as flat as Welsh slate.

You should check the size of the small slates at the verge as they should be a minimum of 150mm wide, slate and halfs are used to obtain this if needed.

If the problem was the structure you would expect to see sweeps in the roof from the ground.

 

[jonez]

Hello!
I'm new to the forum so please forgive possible topic duplication.

I recently contracted a local roofer (via checkatrade - got 3 quotes) to strip, felt and slate my 1930's bungalow which previously had french clay interlocking tiles leaking all over the place.

I opted for natural slate as it is lightweight and looks much better than concrete tiles.

The roofer has almost finished (after being delayed by the awful weather) so today I went up onto the scaffold to inspect the work. Unfortunately the results are frankly shocking. The house is over 85 years old and I appreciate that the roof structure isn't going to be true and flat. However, the newly slated roof is humped and dipped in various places and the majority of the slates do not sit flat, kick up (by more than an inch) and some slates are already broken, chipped and don't butt up laterally (pictured below)

Am I wrong in thinking a competent roofer is able to compensate for uneven substrate with proper measurement and workmanship (to a certain degree)? Isn't the roofer supposed to sort the slates prior to slating? Isn't the roofer supposed to adjust the battens to compensate for unevenness?

The slates around the velux are kicked up so much I think they would be ripped off by a strong gust of wind. I'm really at a loss as to what to do, because I'm pretty sure he will say its because of the 'old roof' structure and there's nothing he can do (although he didn't mention it would be a problem before). As you can imagine this isn't a cheap job and I don't want to pay the balance until I am satisfied.

I would be really grateful for anyone's opinion as this is really stressing me out.

Thanks in advance for your thoughts.

As others have said that workmanship is poor to the point of being unserviceable. There is some irregularity in the rafters but not so much it should be a problem, the roofer should have corrected any significant changes by notching/packing as appropriate. If there are severe irregularities many roofers will want a joiner to do remedial work before they start but your roof structure doesn't look that bad.

You're right that the slates should be sorted before work starts and that is the most noticeable problem, slates vary in thickness so you have to go through them all and put them into different stacks depending on thickness. Many roofers will gauge into thick/medium/thin although with some batches it's better to select more than three groups. The thickest slates go on first at the eaves, the next thickest when they're used up etc. Some slates may be thicker on one edge than the other and/or be warped and it's part of the roofers skill to make best use of these without disrupting the roof - on the verges for example. It's time-consuming to gauge slates and some roofers don't bother, with results like yours.

When you see poor workmanship like that you wonder what else is wrong and there are a few other things to check. It's not possible to say without measurements but the gauge (pitch) of the slates looks stretched - particularly the eaves course. Slates depend on a double overlap at the top - the headlap. The appropriate headlap varies with local conditions and roof construction but shouldn't be less than 55mm. As a rule of thumb slates are twice as long as their width so if the bit you can see is a square there is zero headlap, if the side of the bit you can see is longer than the width then the headlap is negative. If the headlap is too small the roof will leak although it may not be immediately apparent if the membrane channels the water away.

The head course under the ridge looks too long. To maintain headlap the final course at the top is normally short with the course beneath it sitting on the final lath under the ridge. It's not clear from your pictures but this may not be correct.

Do you know what nails were used? British standard requires copper or aluminium for slates, some roofers skimp and use galvanised nails to save a small amount on the job. Is the membrane in good condition and properly fitted? Of the concerns you mentioned the one I wouldn't worry about is the 'butting up laterally'. Slates are never completely uniform so it's necessary to have a small gap to accommodate variations while keeping the bond between courses correct.

It's impossible to say without a detailed inspection but I wouldn't be paying the balance of the invoice and depending on the outcome of an expert survey would be thinking of having it stripped and done again.

There are a couple of useful guides for slate roofing here..

http://www.sigroofing.co.uk/downloads/naturalslate.pdf

and here..

http://www.welshslate.com/wp-content/uploads/2013/07/roofing_brochure_Jan13.pdf

Tony.

 

[xr4x4]

My cousins a roofer and has done a few roofs for me, manly slate.

He has done a old barn conversion and the roof bent and sagged all over the place, character you might say, even so, the slates where flat once fitted.

Your roofer should of stopped and made you aware if he had problems with the roof, given you the options and the cost implications and allowed you to make the call.

 

[Knottypinehell]

The worst issue is the area around the Velux. As a minimum this area should be stripped off and a proper slate flashing kit installed and area reslated.

The slates seem to be Spanish and Spanish slates are often twisted and do not lay as flat as Welsh slate.

You should check the size of the small slates at the verge as they should be a minimum of 150mm wide, slate and halfs are used to obtain this if needed.

If the problem was the structure you would expect to see sweeps in the roof from the ground.

Thanks for your comment, you are correct, the slates are indeed Spanish and quite thin/brittle. I uploaded a pic of the verge to show the half slates you mention. Do they seem ok?

Also uploaded a close up of the flashing round the velux. As you and Catlad say, this looks wrong. It looks like the original flashing kit from the interlocking tiles. Maybe he hasn't done this yet? He asked me for the GGL number weeks ago so I assumed this would have been done by now. Not sure what point you would do this, but curious why slates are already laid over it.

 

[Knottypinehell]

As others have said that workmanship is poor to the point of being unserviceable. There is some irregularity in the rafters but not so much it should be a problem, the roofer should have corrected any significant changes by notching/packing as appropriate. If there are severe irregularities many roofers will want a joiner to do remedial work before they start but your roof structure doesn't look that bad.

You're right that the slates should be sorted before work starts and that is the most noticeable problem, slates vary in thickness so you have to go through them all and put them into different stacks depending on thickness. Many roofers will gauge into thick/medium/thin although with some batches it's better to select more than three groups. The thickest slates go on first at the eaves, the next thickest when they're used up etc. Some slates may be thicker on one edge than the other and/or be warped and it's part of the roofers skill to make best use of these without disrupting the roof - on the verges for example. It's time-consuming to gauge slates and some roofers don't bother, with results like yours.

When you see poor workmanship like that you wonder what else is wrong and there are a few other things to check. It's not possible to say without measurements but the gauge (pitch) of the slates looks stretched - particularly the eaves course. Slates depend on a double overlap at the top - the headlap. The appropriate headlap varies with local conditions and roof construction but shouldn't be less than 55mm. As a rule of thumb slates are twice as long as their width so if the bit you can see is a square there is zero headlap, if the side of the bit you can see is longer than the width then the headlap is negative. If the headlap is too small the roof will leak although it may not be immediately apparent if the membrane channels the water away.

The head course under the ridge looks too long. To maintain headlap the final course at the top is normally short with the course beneath it sitting on the final lath under the ridge. It's not clear from your pictures but this may not be correct.

Do you know what nails were used? British standard requires copper or aluminium for slates, some roofers skimp and use galvanised nails to save a small amount on the job. Is the membrane in good condition and properly fitted? Of the concerns you mentioned the one I wouldn't worry about is the 'butting up laterally'. Slates are never completely uniform so it's necessary to have a small gap to accommodate variations while keeping the bond between courses correct.

It's impossible to say without a detailed inspection but I wouldn't be paying the balance of the invoice and depending on the outcome of an expert survey would be thinking of having it stripped and done again.

There are a couple of useful guides for slate roofing here..

http://www.sigroofing.co.uk/downloads/naturalslate.pdf

and here..

http://www.welshslate.com/wp-content/uploads/2013/07/roofing_brochure_Jan13.pdf

Tony.

Thanks so much Tony for your detailed reply and the interesting articles. Regarding the headlap, I uploaded a pic of the side of the house. I think this is enough (he said its about 4 inches). However, it looks the same all the way up to the top and not decreasing as you mention.

He said he used 'ali's' which are presumably aluminium nails. Found a few on the floor and took a pic. He quoted for copper nails, so not sure why he's using different or which are better/ more expensive.

You mention getting an expert survey. I would be interested in doing this, but what kind of expert would I get? Another roofer will certainly be able to point out the issues but it wouldn't be worth their while and it's just their word against his. A building surveyor? Someone from the confederation of roofing contractors (of which my roofer is a member)? Someone from building control? (please no!)

Anyway, my roofer is coming back tomorrow (maybe) so I need to be clear on what to say and how to proceed.

Thanks again for clarifying so many things.