Urgent Advice Please - Building Inspector Failed Roof Tiles

[subzero]

Hi we have a major problem. We had an extension built approx 2 years ago and just had the buildings inspector round to perform the final checks and sign-off. On the day all seemed well and he went away happy.

However a couple of days after the visit we received a letter saying that the completion certificate couldn't be issued because the roof tiles need to be replaced as they do not adhere to the British Standard for slating. The roof was completed using 250mm x 400mm slates and apparently this size of slate should not be used on roofs with a pitch of less than 30 degrees (the roof is 20 degrees).

The architects drawing specified that Redland Cambrian slate tiles be used and should be laid at a pitch of approximately 22.5 degrees. The tiles used are slate, but don't think they are Redland Cambrian. This has put us in an awkward situation and expect this will result in a bun fight of some sort.

Many thanks for reading and grateful for any advice.

 

[tony1851]

If your architect's drawing specifies that the slates should be laid to a minimum pitch of 22.5, then that is meaningless. He should have determined the pitch of the roof first, and then specified a tile suitable for that pitch.

Seems like a standard cut-and-paste job where it's not been thought through properly.

If no pitch has been specified, why did the builder do it at 20? And why did he use the slates he did without checking?

Both architect and builder may be at fault here.

 

[Alastairreid]

Cambrians go down to 15 °, your architect specified cambrians which are appropriate for that pitch. sounds like your roofer/builder is at fault here.

http://www.monier.co.uk/products/product-catalogue/product-range/product/cambrian-slate.html

 

[subzero]

Thanks gents, yes we're inclined to agree it's the roofers fault. Just reading the building inspectors letter again and wondering if there's any course for appealing against the decision. The letter does state the the "British Standard for slating RECOMMENDS that the size of slate should not be used on roofs with a pitch of less than 20 degrees". I guess we're clutching at straws but hoping to avoid a major rework, especially since the roof has been in place for two years without any problems whatsoever.

 

[tony1851]

Why has it taken two years for the final inspection?

Presumably the builder won't want to look at it now.

 

[subzero]

It's just taken ages to get other bits done which were also required for the sign-off. Obviously this is a major blow.

 

[Alastairreid]

Cambrians are designed and engineered to work at that low pitch! slate need a minimum pitch of 30-35 ° dependant on headlap to work.

The roof will fail eventually when the membrane starts to degrade.

You wont get a sign off with those slates at that pitch.

The roof should be changed to cambrian...

If you instructed the roofer to use cambrian it is his responsibility to rectify, even if you did not specify the the of slate he has been negligent in his choice as they are not fit for purpose.

 

[tony1851]

If you instructed the roofer to use cambrian it is his responsibility to rectify, even if you did not specify the the of slate he has been negligent in his choice as they are not fit for purpose.

That's right, but getting the roofer to rectify it may be a problem.

 

[Alastairreid]

If you instructed the roofer to use cambrian it is his responsibility to rectify, even if you did not specify the the of slate he has been negligent in his choice as they are not fit for purpose.

That's right, but getting the roofer to rectify it may be a problem.

After 2 yrs next to no chance.

Op be under no illusion the roof will fail! the membrane is doing a job its not designed for.

Post a pic.

 

[tony1851]

The BS may recommend a minimum pitch for that size (assuming we're talking about natural slate). But a BS is not the be-all and end-all; slate is a natural product and will vary in quality.

There is no actual building regulation which states a minimum pitch for slate. The only criteria are that water should be prevented from entering the building, and that materials should not be allowed to decay prematurely.If you have had no problem, why not offer to remove a few slates so that the inspector can have a look at the felting and battens?

If all is well, there seems no reason why you should not get the Cert.

The chief problem may not be rain penetration as such, but rather premature decay of the slate. If the pitch is not sufficient, it tends not to drain as well, and water lingers between the slates, where it can cause problems. Much depends on the exposure of the roof. Are there any valleys? That would not help the situation.

 

[tony1851]

(double).

 

[subzero]

Thank you so much for your kind replies gents. We actually know the builder fairly well and are still in good comms as we have been supplying other work also. So all is not lost there. We never gave any specific instruction other than what was clearly laid out and specified in the architects drawings.

As you say it may well be worth having the inspector look at the battens underneath, but understand that the tiles aren't doing their job at present.

Furrowed brow [ON]...

 

[jonez]

Thank you so much for your kind replies gents. We actually know the builder fairly well and are still in good comms as we have been supplying other work also. So all is not lost there. We never gave any specific instruction other than what was clearly laid out and specified in the architects drawings.

As you say it may well be worth having the inspector look at the battens underneath, but understand that the tiles aren't doing their job at present.

Furrowed brow [ON]...

The key issue for slates laid to BS is to get the headlap and sidelap large enough for the pitch and exposure. 20 degrees is very shallow for a slate roof but BS allows 500x300 to be used with a 115mm headlap in moderate exposure, so that's a reasonable aim.

If you are in a moderate exposure area and the headlap is 115mm or more you could try to agree a variation with the building inspector, if it's less than that it would be difficult to justify.

If the headlap is 115mm on a 400mm slate the height of the visible strip of slate will be 142.5mm - if it's more than that it will need to be redone to be compliant. If it's less than 142.5mm then it is technically non-compliant but you could make a case that it's fit for purpose.