Building regulations for suspended floor insulation

battenburg88

So firstly I know there are a couple of tangents here....one is that the only definitive answer I can get is from my local Building Control office. Unfortunately there is no way of phoning them to have a quick chat - they want queries submitted online with details and photos etc. The second tangent is that if I got underfloor insulation then how would BC know anyway? However, I like to do things by the book.

This is a Victorian terrace with a suspended floor. We are getting the floor levelled and rubble removed from underneath in the hope that ventilation will be improved. There is the possibility of installing insulation between the joists whilst all of the floorboards are up. I know that whether this is a good thing to do is, in itself, slightly contentious, but putting that to one side for the moment.

When this first came up I read the Building Regulations document about energy conservation. My reading was that if you are renovating 50% or more of a thermal element then you should improve the energy efficiency of the whole element i.e. would require a BC notification. My hope with this work is that over 50% of the floor does not need to be renovated or replaced - the floorboards will be lifted and I'm sure there will be some rotten joists ends etc. but, fingers crosses, not more than 50%. I interpreted this as meaning that I do not need to get BC sign off if insulation was installed. 

I was reading something on another forum where someone just said that if you installed underfloor insulation you need to go through BC, end of. This obviously conflicts with my original reading of the document, but I am very much a layperson.

Can anyone help with my understanding? I don't want to avoid BC in order that the job can be bodged - I very much do not want to do something that could result in the causing any damp issues under the floor. But, I would like to avoid BC in terms of cost of the application and the stress of having to sort out the admin. I tend to overthink and find things like very difficult so avoidance of the paperwork is also a factor.

Any suggestions would be great. Or any experiences of how BC operate for this kind of stuff and actually perhaps it wouldn't be that bad other than the application cost. Cheers!

WIAWSNB

I cannot confirm what the best method of insulating a suspended timber floor is, but can say to not bother informing BC about this.

silvercar

You could always do it in 2 parts, so 45% one day and the remainder the next.

HHarry

If you’re improving the ventilation under the floor then damp problems should be avoided.  And if you’ve got the floor up, then adding some insulation is a no-brainer.

As for BC notification (assuming you don’t meet the 50% criteria) - would you get them involved if you were going to add an extra layer of insulation in your loft?  Crack on and get it done, take loads of photo’s so you can show what’s been done to any interested party in the future.

ComicGeek

https://historicengland.org.uk/advice/technical-advice/retrofit-and-energy-efficiency-in-historic-buildings/upgrading-thermal-elements-installing-insulation/insulating-floors-in-historic-buildings/

Have a read through this before doing anything. I wouldn't get BC involved with this, but you need to make sure that it's done properly.

battenburg88

ComicGeek said:

https://historicengland.org.uk/advice/technical-advice/retrofit-and-energy-efficiency-in-historic-buildings/upgrading-thermal-elements-installing-insulation/insulating-floors-in-historic-buildings/

Have a read through this before doing anything. I wouldn't get BC involved with this, but you need to make sure that it's done properly.

Thanks, will have a read later!

 silvercar said:

You could always do it in 2 parts, so 45% one day and the remainder the next.

HHarry said:

If you’re improving the ventilation under the floor then damp problems should be avoided.  And if you’ve got the floor up, then adding some insulation is a no-brainer.

As for BC notification (assuming you don’t meet the 50% criteria) - would you get them involved if you were going to add an extra layer of insulation in your loft?  Crack on and get it done, take loads of photo’s so you can show what’s been done to any interested party in the future.

Sorry, my quoting got a bit muddled on these two comments!

I know the general advice so far is not to worry about BC, but I'm still interested in this concept of 50% renovation. The purpose of lifting the boards in the first place is to clear out a huge load of builder's waste that seems to have been dumped under there from previous work. As you say, whilst the boards are up then seems as though levelling the floor a bit and insulating are a sensible thing to do. 

But even if all the boards are lifted, I'm hoping that the vast majority will just go back down. Save for perhaps replacing a few rotten joist ends if I'm lucky. Surely just lifting all the floorboards isn't > '50%' renovation. And then that would return me to my original train of thought where BC don't need to be involved. 

WIAWSNB

I have to say it never occurred to me that 'floors' were included in that BC maxim - normally it's walls and roofs - although I guess it makes sense that they are.

However, as others above suggest, get this done for the 'right' reasons - which you appear to be doing. To involve BC in this will almost certainly be an unnecessary expense and complication. 

Eg: they could insist on a level of insulation that's near-bonkers and costly, and that could make you regret ever starting the project, or continuing with it over other floors. 

Read the best way to add insulation to your suspended floor, and this will undoubtedly be transformative in both cutting down draughts and reducing heat loss. 

smilingwarthog

You shouldn't need BC. As others have said, insulation will make a huge difference along with improving the ventilation. There are some helpful guides online, check out Retrovive for example