We have just had the shell of an extension built which includes a flat roof.. Firring strips have been used to produce a fall to one side however this fall is around 20mm over the 3000mm span i.e. 1:150.

Everything I am reading states that, as per BS6229, flat roofs should have a minimum fall of 1:80 (i.e. 37.5mm in my case) and really ought to be designed for 1:40 (75mm) to allow for inaccuracies in construction, settlement of materials etc.

Unfortunately I have only just spotted this and the roof covering (consisting of OSB sheets, vapour barrier, 125mm solid board insulation, ply and a polyurethane liquid membrane) along with cavity trays and flashing all now in place.

Now I'm fretting about possible issues in the future. Am I right to be worried? Should I be seeking this being altered? I was going to speak to Building Control tomorrow to say what they say but whilst they might confirm the fall is low I can't see anything in the regs that mandates a fall and I don't know whether BS6229 is mandatory either (it seems more of a code of practice).

Grateful for your thoughts.

P.S. For what it's worth I must admit to having a tendency to worry - to the point of anxiety - about detail like this.

Mathew Newton Wrote in message:
We have just had the shell of an extension built which includes a flat roof. Firring strips have been used to produce a fall to one side however this fall is around 20mm over the 3000mm span i.e. 1:150.

Everything I am reading states that, as per BS6229, flat roofs should have a minimum fall of 1:80 (i.e. 37.5mm in my case) and really ought to be designed for 1:40 (75mm) to allow for inaccuracies in construction, settlement of materials etc.

Unfortunately I have only just spotted this and the roof covering (consisting of OSB sheets, vapour barrier, 125mm solid board insulation, ply and a polyurethane liquid membrane) along with cavity trays and flashing all now in place.

Now I'm fretting about possible issues in the future. Am I right to be worried? Should I be seeking this being altered? I was going to speak to Building Control tomorrow to say what they say but whilst they might confirm the fall is low I can't see anything in the regs that mandates a fall and I don't know whether BS6229 is mandatory either (it seems more of a code of practice).

Grateful for your thoughts.

P.S. For what it's worth I must admit to having a tendency to worry - to the point of anxiety - about detail like this.


How much of an upstand is there against the "host" wall?
What are the chances of water building up on your flat roof to
overtop the upstand?
--
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On Thursday, 13 September 2018 21:48:21 UTC+1, JimK wrote:

How much of an upstand is there against the "host" wall?

Good question - I haven't (yet) seen how tall the upstand is as it is covered by the lead flashing (which itself looks to be about 150mm and so I know it's less than that).

What are the chances of water building up on your flat roof to
overtop the upstand?

I'd all honesty I'd say there was very little, if any, chance of that happening. There *is* definitely a fall on the roof and whilst there is still a 200kg roof lantern to go on (hence there may be some deflection of the joists) I don't think I'd ever see water running the 'wrong' way. I think by biggest concern is pooling, particularly once the roof gets dirty and weathered, and the increased risk of the membrane failing.

Incidentally, speaking of the membrane, the BBA certificate for its states that 'for the purposes of this certificate flat roofs are defined as those having a minimum finished fall of 1:80' and so I am assuming from this that the approval the certificate assures in terms of regulation compliance could well be not valid if the product has not been installed in accordance with this?

On Thursday, 13 September 2018 22:21:13 UTC+1, Mathew Newton wrote:
On Thursday, 13 September 2018 21:48:21 UTC+1, JimK wrote:

How much of an upstand is there against the "host" wall?

Good question - I haven't (yet) seen how tall the upstand is as it is covered by the lead flashing (which itself looks to be about 150mm and so I know it's less than that).

What are the chances of water building up on your flat roof to
overtop the upstand?

I'd all honesty I'd say there was very little, if any, chance of that happening. There *is* definitely a fall on the roof and whilst there is still a 200kg roof lantern to go on (hence there may be some deflection of the joists) I don't think I'd ever see water running the 'wrong' way. I think by biggest concern is pooling, particularly once the roof gets dirty and weathered, and the increased risk of the membrane failing.

Incidentally, speaking of the membrane, the BBA certificate for its states that 'for the purposes of this certificate flat roofs are defined as those having a minimum finished fall of 1:80' and so I am assuming from this that the approval the certificate assures in terms of regulation compliance could well be not valid if the product has not been installed in accordance with this?

of course


NT

Mathew Newton Wrote in message:
On Thursday, 13 September 2018 21:48:21 UTC+1, JimK wrote:

How much of an upstand is there against the "host" wall?

Good question - I haven't (yet) seen how tall the upstand is as it is covered by the lead flashing (which itself looks to be about 150mm and so I know it's less than that).

What are the chances of water building up on your flat roof to
overtop the upstand?

I'd all honesty I'd say there was very little, if any, chance of that happening. There *is* definitely a fall on the roof and whilst there is still a 200kg roof lantern to go on (hence there may be some deflection of the joists)

How long are these joists?
Is the lantern going mid span?
Is all this by one building outfit?
--
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On Thursday, 13 September 2018 22:31:33 UTC+1, JimK wrote:

How long are these joists?
Is the lantern going mid span?

The joists are 3000mm (or thereabouts) in length, and of 170mm x 50mm C24 timber. The headers and trimmers around the mid-span lantern opening are tripled-up and bolted together. I am expecting deflection to be minimal.

Is all this by one building outfit?

Yes, there is just the one builder (bar the sub-contractor that applied the membrane coating) and he has constructed the shell - responsibility for the lantern, doors and all internal work now rests with me. I am a keen DIYer but I can't build walls and don't have the confidence for the knock-through and working with large steels hence why I got a builder in to do all that (doing the roof seemed more a natural fit for him and the completion of his work too).

Mathew Newton Wrote in message:
On Thursday, 13 September 2018 22:31:33 UTC+1, JimK wrote:

How long are these joists?
Is the lantern going mid span?

The joists are 3000mm (or thereabouts) in length, and of 170mm x 50mm C24 timber. The headers and trimmers around the mid-span lantern opening are tripled-up and bolted together. I am expecting deflection to be minimal.

Is all this by one building outfit?

Yes, there is just the one builder (bar the sub-contractor that applied the membrane coating) and he has constructed the shell - responsibility for the lantern, doors and all internal work now rests with me. I am a keen DIYer but I can't build walls and don't have the confidence for the knock-through and working with large steels hence why I got a builder in to do all that (doing the roof seemed more a natural fit for him and the completion of his work too).


So to building regs?
--
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On 13/09/2018 22:21, Mathew Newton wrote:
On Thursday, 13 September 2018 21:48:21 UTC+1, JimK wrote:

How much of an upstand is there against the "host" wall?

Good question - I haven't (yet) seen how tall the upstand is as it is covered by the lead flashing (which itself looks to be about 150mm and so I know it's less than that).

What are the chances of water building up on your flat roof to
overtop the upstand?

I'd all honesty I'd say there was very little, if any, chance of that happening. There *is* definitely a fall on the roof and whilst there is still a 200kg roof lantern to go on (hence there may be some deflection of the joists) I don't think I'd ever see water running the 'wrong' way. I think by biggest concern is pooling, particularly once the roof gets dirty and weathered, and the increased risk of the membrane failing.

Incidentally, speaking of the membrane, the BBA certificate for its states that 'for the purposes of this certificate flat roofs are defined as those having a minimum finished fall of 1:80' and so I am assuming from this that the approval the certificate assures in terms of regulation compliance could well be not valid if the product has not been installed in accordance with this?

So there is your answer. Your contractor should either increase the fall
or source a membrane that is suitable.

Is there sufficient height at the wall upstand to increase it?

Mike

On Friday, 14 September 2018 08:27:46 UTC+1, Muddymike wrote:

So there is your answer. Your contractor should either increase the fall
or source a membrane that is suitable.

Is there sufficient height at the wall upstand to increase it?

Yes, I think so.

We'd only be looking for an additional 20mm-60mm which I am sure could be accommodated as there are 150mm lead flashings extending above the finished surface.

On Thursday, 13 September 2018 21:14:29 UTC+1, Mathew Newton wrote:
We have just had the shell of an extension built which includes a flat roof. Firring strips have been used to produce a fall to one side however this fall is around 20mm over the 3000mm span i.e. 1:150.

Everything I am reading states that, as per BS6229, flat roofs should have a minimum fall of 1:80 (i.e. 37.5mm in my case) and really ought to be designed for 1:40 (75mm) to allow for inaccuracies in construction, settlement of materials etc.

Unfortunately I have only just spotted this and the roof covering (consisting of OSB sheets, vapour barrier, 125mm solid board insulation, ply and a polyurethane liquid membrane) along with cavity trays and flashing all now in place.

Now I'm fretting about possible issues in the future. Am I right to be worried? Should I be seeking this being altered? I was going to speak to Building Control tomorrow to say what they say but whilst they might confirm the fall is low I can't see anything in the regs that mandates a fall and I don't know whether BS6229 is mandatory either (it seems more of a code of practice).

Grateful for your thoughts.

P.S. For what it's worth I must admit to having a tendency to worry - to the point of anxiety - about detail like this.

IIRC some of the first flat roofs were fully flat with a lip all round. The intention was they held a thin layer of water which somehow protected the felt. Needless to say that method was replaced, the first slight hole and it all went in there.

I don't see BR helping you.


NT

On Thursday, 13 September 2018 22:07:21 UTC+1, wrote:

I don't see BR helping you.


NT

Even if they were to say 'theres nothing explicit in the regs but if I were you I wouldnt lose sleep over it' that in itself would actually be of considerable help!

On Thursday, 13 September 2018 22:23:04 UTC+1, Mathew Newton wrote:
On Thursday, 13 September 2018 22:07:21 UTC+1, wrote:

I don't see BR helping you.


NT

Even if they were to say 'theres nothing explicit in the regs but if I were you I wouldnt lose sleep over it' that in itself would actually be of considerable help!

A bit of an update:

I spoke to Building Control this morning and whilst my inspector is away in holiday one of his colleagues listened to what I had to say. Based on that, and that alone, his view was that the fall was indeed unsatisfactory and could well be considered a violation of the regs. He confirmed there was nothing explicitly stated about falls in them but there is something of a catchall 'quality and workmanship' requirement which generally requires, amongst other things, compliance with relevant standards where appropriate to demonstrate compliance. Hence, the British Standard would be relevant here, not least given how accepted its fall figures are in the industry.

He did also say they'd need to see it really as there may well be a good reason why it is the way it is, and if there is then they would always try and take a pragmatic approach towards consideration of accepting it as they don't like to insist on re-work if not absolutely essential. He did echo my concerns though about the fact that the roof lantern is yet to be installed and so any test of falls at the moment could be premature.

I then spoke to the builder who was, thankfully, very considerate of my concerns. He immediately said he wondered if he might've made a mistake in the calculations but obviously couldn't really comment further without first coming to see what's what. He's away on holiday so next week we are going to meet up.

The builder confirmed that the furring strips weren't off-the-shelf and so this in my view might explain how the mistake might've occurred as I'm sure we have all performed a calculation, been happy with the result but then realised once you'd built the damn thing you'd made an error (or indeed not realised until someone else points it out!.

So we are on pause until next week but so far so good. As things stand I see no alternative but to strip and re-build as I can't see myself accepting the current construction and it sounds like BC might not either. It is unfortunate but mistakes do happen and I am currently content to consider it as just that.

Mathew Newton Wrote in message:
On Thursday, 13 September 2018 22:23:04 UTC+1, Mathew Newton wrote:
On Thursday, 13 September 2018 22:07:21 UTC+1, wrote:

I don't see BR helping you.


NT

Even if they were to say 'theres nothing explicit in the regs but if I were you I wouldnt lose sleep over it' that in itself would actually be of considerable help!

A bit of an update:

I spoke to Building Control this morning and whilst my inspector is away in holiday one of his colleagues listened to what I had to say. Based on that, and that alone, his view was that the fall was indeed unsatisfactory and could well be considered a violation of the regs. He confirmed there was nothing explicitly stated about falls in them but there is something of a catchall 'quality and workmanship' requirement which generally requires, amongst other things, compliance with relevant standards where appropriate to demonstrate compliance. Hence, the British Standard would be relevant here, not least given how accepted its fall figures are in the industry.

He did also say they'd need to see it really as there may well be a good reason why it is the way it is, and if there is then they would always try and take a pragmatic approach towards consideration of accepting it as they don't like to insist on re-work if not absolutely essential. He did echo my concerns though about the fact that the roof lantern is yet to be installed and so any test of falls at the moment could be premature.

I then spoke to the builder who was, thankfully, very considerate of my concerns. He immediately said he wondered if he might've made a mistake in the calculations but obviously couldn't really comment further without first coming to see what's what. He's away on holiday so next week we are going to meet up.

The builder confirmed that the furring strips weren't off-the-shelf and so this in my view might explain how the mistake might've occurred as I'm sure we have all performed a calculation, been happy with the result but then realised once you'd built the damn thing you'd made an error (or indeed not realised until someone else points it out!.

So we are on pause until next week but so far so good. As things stand I see no alternative but to strip and re-build as I can't see myself accepting the current construction and it sounds like BC might not either. It is unfortunate but mistakes do happen and I am currently content to consider it as just that.


Be interested in updates on outcome of this &, essentially, who
ends up paying/ giving in...
--
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On Friday, 14 September 2018 22:05:16 UTC+1, JimK wrote:

Be interested in updates on outcome of this &, essentially, who
ends up paying/ giving in...

The builder visited today€¦

He was actually very good about the situation and quickly held his hands up once hed checked and measured the firring strips himself. Whilst the finished roof does drain, and in his opinion wouldnt prematurely leak, he acknowledged that its fall was below-spec it was my prerogative to be concerned and to expect a remedy. To this end we came up with a few options; the choice of which is entirely mine and he will pick up the bill:


1. Leave As-Is €“ He would give me a guarantee in writing that should the roof fail in the next x years (to be agreed) he would repair/replace and make good any consequential damage. To give me greater confidence he could also get the roofer to add another layer of the liquid membrane to the existing. He would also refund the initial £1000 roofer cost.

2. Remove and Rebuild €“ Rip up the entire roof deck (membrane and trims, top boards, insulation, bottom boards and firring strips) and replace (likely with bought firring strips this time €“ he had no idea they were available off-the-shelf hence why he always cut his own, normally without making a mistake with the measurements!)

3. Overboard and Recoat €“ Keep the old roof in place (bar the trims), add a new layer of OSB3 on top of suitable firring strips to give the correct fall and put a new waterproof coating on top.

I am not comfortable with option 1 as whilst I trust his word regarding the guarantee (we live in a small town, him and his son just down the road from me; theres nowhere to hide!) my preference here is to avoid a leak in the first place rather than deal with one if/when it happens. Id also like to draw a line under the situation rather than leave things hanging over me/us.

Option 2 was my initial preference as this gets me back to the position I was in before the mistake happened and therefore not be considered a €˜bodge in any way. However, his initial thoughts were that it could cause more problems than it solves. We didnt get into too much detail about it but his concerns were about the destruction required as with all the fixings now hidden thered likely be a lot of €˜coercion of materials and could lead to damaging other components. Might be worth pushing further though, particularly as I'd be more than happy to help with the removal side.

Option 3 sounds like a viable option as not only does it give me the opportunity for a new waterproof coating (I am leaning more towards a single-sheet EPDM membrane rather than another liquid coating - ever since it went on my confidence in it has not been the greatest as it is far from conventional and so seemingly not much information about it) but the extra board/membrane layer may also provide an additional noise and solar barrier? I certainly wouldnt ever expect a leak through two surfaces either, at least not down into the living space! I am wondering about potential downsides though... It would add ~50mm to the roof height at the rear wall abutment which would eat into the 150mm lead flashing and the roof lantern upstand would require extra timber on top to increase its standoff height. Could there be a risk of interstitial condensation with this extra layer or would it be okay given it is on the cold side of the insulation? Should the gaps between the firring strips be filled with anything? (Note the strips will likely be 40mm to zero over a 3m span so not much volume there).

As before I would be grateful for your thoughts. The builder is being completely open and supportive of the situation and keen to make sure I am happy with the outcome €“ I just need to work out what the best outcome should be!

Yes my neighbour many years ago did their build using family members and of
course now the new owners have always had puddling and leaks despite several
re applications of the outer surface etc.
Obviously it took many years and you cannot prove a negative in that had it
had a greater slope, would it have fared better in the same time scale, but
it is a little worrying, and I do wonder if anyone actually checks this sort
of thing properly.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Mathew Newton" wrote in message
...
We have just had the shell of an extension built which includes a flat roof.
Firring strips have been used to produce a fall to one side however this
fall is around 20mm over the 3000mm span i.e. 1:150.

Everything I am reading states that, as per BS6229, flat roofs should have a
minimum fall of 1:80 (i.e. 37.5mm in my case) and really ought to be
designed for 1:40 (75mm) to allow for inaccuracies in construction,
settlement of materials etc.

Unfortunately I have only just spotted this and the roof covering
(consisting of OSB sheets, vapour barrier, 125mm solid board insulation, ply
and a polyurethane liquid membrane) along with cavity trays and flashing all
now in place.

Now I'm fretting about possible issues in the future. Am I right to be
worried? Should I be seeking this being altered? I was going to speak to
Building Control tomorrow to say what they say but whilst they might confirm
the fall is low I can't see anything in the regs that mandates a fall and I
don't know whether BS6229 is mandatory either (it seems more of a code of
practice).

Grateful for your thoughts.

P.S. For what it's worth I must admit to having a tendency to worry - to the
point of anxiety - about detail like this.

"Mathew Newton" wrote in message
...
We have just had the shell of an extension built which includes a flat roof.
Firring strips have been used to produce a fall to one side however this
fall is around 20mm over the 3000mm span i.e. 1:150.

Everything I am reading states that, as per BS6229, flat roofs should have a
minimum fall of 1:80 (i.e. 37.5mm in my case) and really ought to be
designed for 1:40 (75mm) to allow for inaccuracies in construction,
settlement of materials etc.

Unfortunately I have only just spotted this and the roof covering
(consisting of OSB sheets, vapour barrier, 125mm solid board insulation, ply
and a polyurethane liquid membrane) along with cavity trays and flashing all
now in place.

Now I'm fretting about possible issues in the future. Am I right to be
worried? Should I be seeking this being altered? I was going to speak to
Building Control tomorrow to say what they say but whilst they might confirm
the fall is low I can't see anything in the regs that mandates a fall and I
don't know whether BS6229 is mandatory either (it seems more of a code of
practice).

Grateful for your thoughts.

P.S. For what it's worth I must admit to having a tendency to worry - to the
point of anxiety - about detail like this.

well Scottish building regs ...when regs used to make sense....used to say a
flat roof should be over 1:10 .... if it is any help....so 1:8 sound OK
........don't worry...be happy.....

On Friday, 14 September 2018 08:34:05 UTC+1, Mannequin of mirth ... wrote:

well Scottish building regs ...when regs used to make sense....used to say a
flat roof should be over 1:10 .... if it is any help....so 1:8 sound OK
.......don't worry...be happy.....

1:10? That's not a flat roof.

Not sure what you mean with the 1:8 reference - ours is 1:150.