Building Control, small lean-to roof, rafter replacement

hatt55

I'll preface this with saying that I know this kind of work gets done without telling Building Control. But I'd really like the paperwork to be in order and it feels like this could be more straightforward than I'm managing to make it. By local BC have also proved very difficult to just call and have an informal chat with, because that would be a great option if available! I will try that again on Monday anyway.

Lean-to utility room on the back of a Victorian terrace. Single skin brick and no insulation in the roof and damage to the ceiling. I'm finally getting a builder to come and install insulation and a Velux window for a bit more light. Because the existing rafters are quite shallow and the area of the roof is small (3x3m ish) they advised just replacing the woodwork and membrane which is all pretty old, which will allow a better depth of insulation. My understanding is that it is effectively like for like and there is no structural need for it, other than they might be able to make the spacing match the Velux window. They will also replace the plasterboard ceiling and an electrician will put a couple of lights in. The same tiles will go back on so no change in weight.

I thought that this level of of minor work could be covered by a Building Notice and I would just write a narrative description of what was being done and submit that to the council. It could be submitted a few days before the work starts. This evening I asked ChatGPT to turn the quote from the builder into some sensible text I could send to BC if needed, and then was getting a bit more info on the process. It suggested that because replacing rafters is effectively structural, I might need do a full plans application!

I'm hoping this is one of those instances where AI isn't talking sense. But, if its correct then I'm a bit worried because there are no formal plans - this is just me asking a builder to insulate the roof/repair the ceiling of a really cold room. A full plans application also throws up some terrifying terms like Principal Designer and Contractor.

Can any help advise? Other than the obvious "BC don't need to know about this". Does something count as being structural if you're just replacing what was already there? Well, replacing with slightly bigger rafters, in order to accommodate better insulation.

stuart45

You are putting a roof window in, so the structure of the roof is being changed. You can do this off a Building Notice though. There will be a bit more weight transferred to the wall plate as well.

hatt55

stuart45 said:

You are putting a roof window in, so the structure of the roof is being changed. You can do this off a Building Notice though. There will be a bit more weight transferred to the wall plate as well.

Thanks for the response. You see that I've woken up very early to see if there were any responses, as this is now causing me worry!

In terms of the wallplate, do you know if is this something that would require formal structural calculations? I see that there are various online span tables, based on the pitch of the roof and length of the span. These seem fairly straightforward, but I don't see mention of a wallplate. Though, I'm not a builder so I don't really know whether such a thing is 'calculated'.

When I was thinking about this before, I got myself tied up knots because I started to think that if it became classed as structural, they would want to know things like the type of foundation and they would end up asking me to rebuild the whole room (its clearly not bee constructed that well, but probably 60 years ago).

Edit: I'll add to this that I've just done some quick measurements and the angle of the roof is about 25 degree, the span is 2.1m and the width is approx. 3m (didn't actually measure that one). It sounds like the proposed 200mm x 50mm rafters are fine, potentially excessive in terms of sturcture for the roof element. And potentially 600mm spacing. Perhaps its such a simple structure that even me doing these hand calcs is sufficient....

stuart45

I wouldn't worry too much. When you put a Building Notice in the Building Inspector will explain what he wants. It's normally straightforward to do.

WIAWSNB

stuart45 said:

I wouldn't worry too much. When you put a Building Notice in the Building Inspector will explain what he wants. It's normally straightforward to do.

That would be great, but is it correct? (I don't know - I'm asking).

It certainly wasn't when sil had an internal wall taken down a few years back.

The BCO was fine - very helpful. But he wouldn't commit to any input or opinion, but only that we'd need an SE to confirm whether structural, and then to calculate a suitable lintel. And that was all perfectly fine; he got the SE report, came out to confirm it was as described, and ticked it off.

So what would you expect the BCO to say in this case? Is he really going to discuss the 'beefing up' of the existing joists, the required level of joist sistering around the skylight, the type of roof to be used - warm or cold - and the construction of each, including insulation levels, vapour barriers, ventilation?

I just don't see that happening. 

Does anyone know how this will turn out if Hatt applies for a Building Notice? 

silvercar

The risk is always the BC require you to do things to a higher standard than you were intending. You may have been happy with an improvement on the current situation, but BC may insist on meeting certain regulation on insulation of the wall or roof beyond what you can afford, with knock on works required eg to support the high roof insulation required may require stronger foundations. 

This is why some people just get stuff done, happy in the knowledge they are improving on the current situation, even if it doesn't meet current building regs. 

WIAWSNB

If you go small works 'building notice', then you will end up with a fully compliant construction.
But, your builder will need to fully comply with current regs.
At a guess, this will require him demonstrating that the modifications he is intending for the roof joists will be acceptable. Or, he builds a completely new roof from scratch.
You may wish to check what this involves, and what the resulting cost will be.
Skylights also need to conform, as will their installation - again adequate insulation to the raised sides, bolstered supporting joists, etc.
And I imagine they will be concerned about the outer finish, and whether that also meets current standards?
So, make sure that (a) your builder is au fait with these regs, since the BCO will be checking up on it, and (b) what the cost of a roof built to full current standards will be.

And (c), check what the actual tangible difference will be between what your builder is currently proposing, and a fully compliant version.

I cannot see your BCO - unless they happen to be the most engaging and helpful on the planet - standing there with your builder and discussing his proposal; he will surely expect a detailed, evidenced, spec, and will check that this is being followed. 

NB. I am not suggesting you just 'go' with your builder's proposals, and certainly not unless you are absolutely happy to, and are convinced by him that his proposal will barely be a compromise. 

I wouldn't anticipate any issues when you come to sell - if asked, you just explain the roof was refurbished/updated/whatevs, and not a 'replacement'. But that you still went to considerable lengths to ensure it's of a high standard of insulation and stuff - you can show some pics. It'll be like any other part of your house; "Is your hipped roof compliant with current regs?" "No idea. All I know is that it's in good order, and hasn't fallen down in 40 years..."

IF the added cost of going 'full compliance' is relatively marginal, then absolutely go for it. I doubt it will be, tho'. I expect it'll be double, or more.

Personally, and this is just my personal take, I would spend that extra money on lining the insides of your single skin walls with insulated plasterboard, and really making a difference to that room. Win-win.

I see it like this; you currently have a clearly not remotely up to current regs lean to, and one that makes this clear - I bet it's bludy freezing! Your choice is to follow BC regs at great cost which, unless you can actually afford it, will mean a compromise elsewhere, such as in the walls. Or, use your builder's evidenced judgement - ie he needs to explain the level of actual insulation he proposes, coupled with an understanding of the roof construction - and use the difference to consider improving the wall insulation. 

For the same money, I'm pretty sure I know which option will improve that room the most, and by a significant margin.

In your boots, I'd only go full compliance if I 'needed' to - eg it could affect an imminent sale - or if the added cost was reasonable and acceptable, and if I also had enough money to update the rest of the room too. 

I would personally not go for full compliance on this roof if it meant I couldn't then update the walls as well. Or it caused any other unacceptable-to-me compromise.

This is how insulation works; Add one inch of PIR to a single skin wall and you will utterly transform its insulation value. The difference will be tangible; you will both feel it, and see it in your gas bill*. Add two inches, and - wow - that's better still. 3, and, um, yes, I think my bill is slightly less than before. 4? Meh. 6? What I do notice is that my room is smaller than it was before...

*When I converted our single-skin attached garage into the room I am currently sitting at, I used 1" battens in-filled with 1" Jablite (expanded polystyrene!), and then overboarded with 1" insulated plasterboard. It is the cosiest room in the house, and the easiest to heat; before I swapped the old 42" Plasma TV I used to have as a PC monitor for the 32" LCD I currently have, the TV kept the room warm even in winter. Now, the rad is cracked open to a luke-warm trickle. 

stuart45

WIAWSNB said:

stuart45 said:

I wouldn't worry too much. When you put a Building Notice in the Building Inspector will explain what he wants. It's normally straightforward to do.

That would be great, but is it correct? (I don't know - I'm asking).

It certainly wasn't when sil had an internal wall taken down a few years back.

The BCO was fine - very helpful. But he wouldn't commit to any input or opinion, but only that we'd need an SE to confirm whether structural, and then to calculate a suitable lintel. And that was all perfectly fine; he got the SE report, came out to confirm it was as described, and ticked it off.

So what would you expect the BCO to say in this case? Is he really going to discuss the 'beefing up' of the existing joists, the required level of joist sistering around the skylight, the type of roof to be used - warm or cold - and the construction of each, including insulation levels, vapour barriers, ventilation?

I just don't see that happening. 

Does anyone know how this will turn out if Hatt applies for a Building Notice? 

I've done quite a few jobs off a Building Notice over the years, and normally just discuss the job with the BCO. There will always be certain structural aspects that require an SE, but usually he will just say what's required at each stage of the build. 
If Hatt applied for a Building Notice it really depends on the individual BCO on what he wants. In this case I'd say he will probably explain about the double rafters and trimmers for the window and level of insulation for the roof.
I've built extensions off a Building Notice without the need for an SE.

Section62

WIAWSNB said:

stuart45 said:

I wouldn't worry too much. When you put a Building Notice in the Building Inspector will explain what he wants. It's normally straightforward to do.

That would be great, but is it correct? (I don't know - I'm asking).

It certainly wasn't when sil had an internal wall taken down a few years back.

The BCO was fine - very helpful. But he wouldn't commit to any input or opinion, but only that we'd need an SE to confirm whether structural, and then to calculate a suitable lintel. And that was all perfectly fine; he got the SE report, came out to confirm it was as described, and ticked it off.

...

...Which was the BCO explaining what he wants.  I.e. that a SE has looked after the structural side of things.

The BCO isn't (usually) a qualified structural engineer, therefore cannot advise on structural matters.

With the building notice route the onus is on the people doing the work to be competent and do the job to (at least) comply with standards.  If the BCO isn't happy, the work has to be redone.

The only significant difference with the full plans route is with approved plans you get an opinion at the start that if built according to the plans then it will be compliant and signoff should be a formality.

I think stuart45 is correct - the OP shouldn't worry too much.  Standard tables can be used to confirm the new rafters are adequate. The BCO might ask for a SE opinion on the adequacy of the wall plate, or that the builder simply replaces that as well. Getting the insulation and ventilation correct is probably the bigger challenge - which is where the competency of the builder is the key thing.

WIAWSNB

Cool - always best to go BC if you can.

But, the OP should know the potential pros and cons. 

Section62

WIAWSNB said:

...

I see it like this; you currently have a clearly not remotely up to current regs lean to, and one that makes this clear - I bet it's bludy freezing! Your choice is to follow BC regs at great cost which, unless you can actually afford it, will mean a compromise elsewhere, such as in the walls. Or, use your builder's evidenced judgement - ie he needs to explain the level of actual insulation he proposes, coupled with an understanding of the roof construction - and use the difference to consider improving the wall insulation. 

For the same money, I'm pretty sure I know which option will improve that room the most, and by a significant margin.

In your boots, I'd only go full compliance if I 'needed' to - eg it could affect an imminent sale - or if the added cost was reasonable and acceptable, and if I also had enough money to update the rest of the room too. 

I would personally not go for full compliance on this roof if it meant I couldn't then update the walls as well. Or it caused any other unacceptable-to-me compromise.

...

Might just be worth reminding folk that compliance with the building regs isn't optional... you don't get to decide to ignore them in order to spend the money on something you personally consider to be more worthwhile.

Non-compliance with the regs is a criminal offence.  With the potential for unlimited fines and/or up to two years in jail.  Plus up to 10 years for enforcement action to be taken.

Sure, lots of work gets done which doesn't comply with the regs. But let's not confuse that with building regs compliance being optional.