My suspended floor insulation work started properly last week - before then lots of prep. A few days before the insulation work started I discovered that floor insulation now requires building control approval (Building Regs Part L). I tried to contact Manchester City Council before the insulation work started to find out what I need to provide, but I still haven’t had any answers.
Has anyone else had to deal with MCC re suspended floor insulation? If so, what information was required in order to apply?
I’ve looked into this a bit and found
If building work consists only of installing certain types of services or fittings (e.g. fuel-burning appliances or replacement windows) and the building owner employs an installer that is registered with a relevant competent person scheme designated in the regulations, a building control body does not need to be notified.
For further information about competent person schemes, see Chapter 5 in Volume 1 and Chapter C in Volume 2 of the Manual to the Building Regulations.|
So the first stop is to find out whether your installer is a registered competent person permitted to self approve new floors.
I also found that if replacing a floor the maximum permitted U value is now 0.18W/(m²K).
Thanks Tim.
The council have just today sent me some pdf forms which are slightly clearer than the online versions which were very unclear. It looks as if it’s just Building Notice (no pland needed). But they haven’t explained which form I fill in and when, how much it will cost, or what evidence I will need to provide. All very vague… This is what I’m struggling with most.
The installer isn’t registered as a competent person (although I’m satiisfied he is competent!).
Part L has
Table 4.2 Limiting U-values for new fabric elements in existing dwellings - floor u-value 0.18W/(m²K) and
Table 4.3 Limiting U-values for existing elements in existing dwellings - floor u-value 0.25W/(m²K)
I’m assuming Table 4.3 since these are replacement floors not new floors.
“If achieving the U-value in Table 4.3, column (b) either: a. is not technically or functionally feasible or b. would not achieve a simple payback of 15 years or less then the element should be upgraded to the lowest U-value that both: a. is technically and functionally feasible and b. can achieve a simple payback not exceeding 15 years.”
We won’t be hitting the required u-value because of joist depth and using wood-fibre, and payback will exceed 15 years…
My understanding is that if you insulate the existing floor the 0.25W/m²K applies but if you build a new floor the 0.18W/m²K applies.
It is similar regulations that apparently mean that flat roofs virtually never get replaced any more. Even the most drastic work is treated as a repair to avoid the cost of enhancements.
Those figures are average for the whole floor, so if the subfloor is uneven you can compensate in deeper areas and skimp in shallower ones, but aside from the regulations you don’t want too much variation for comfort.
Regarding the MCC forms and procedures I’m afraid I can’t help as I am not in the area.
I wonder how building a new floor is defined? If you lift floorboards, insulate and then replace the floorboards is that a new floor? If you lift plywood, some parts of which are rotting, insulate and then partly replace/partly install new ply is that a new floor?
This Local Authority Building Control web page suggests not? But perhaps I’m misinterpreting…
What do you believe the U value will be when work is complete? The question of which regulation applies is hopefully just academic. I’m aiming for under 0.1W/m²h, with a completely new floor, done in two or three zones, depending on what I discover as I go.
It will be mostly 0.30W/m2k but 0.23W/m2k in one room where joists are deeper.
I’ve just gone back to Part L and sections 11.2 and 11.3 say:
11.2 Renovation of a thermal element means one of the following.
a. Providing a new layer through cladding or rendering the external surface of a thermal element.
b. Providing a new layer through dry-lining the internal surface of a thermal element.
c. Replacing an existing layer through stripping down the element to expose basic structural components (e.g. bricks, blocks, rafters, joists, frame) and then rebuilding.
d. Replacing the waterproof membrane on a flat roof.
e. Providing cavity wall insulation.11.3 If a thermal element is renovated and one of the following applies, then the whole of the thermal element should be improved to achieve at least the U-value given in Table 4.3, column (b).
a. More than 50% of the surface of the individual thermal element is renovated (see paragraph 11.4).
b. The work constitutes a major renovation. A major renovation is when more than 25% of the surface area of the external building envelope is renovated.
so I’ve assumed that since we are exposing joists and then rebuilding, that it’s Table 4.3 which is relevant and not Table 4.2 - and the Table 4.3 ‘Improved’ floor u-value is 0.25W/m2K.
Fortunately the regulations appear to have exemptions related to practicality, so in practice with an old house of uncertain construction detail you should be able to get away with quite a lot. Otherwise you will need to fix battens under the joists to extend their depth for insulation.
After some toing and froing the council sent me Building Notice and Commencement Notice forms by email (the online forms don’t seem to work for ‘renovation of thermal elements’). I completed and submitted both at the same time, since work had already begun, paid my fee and was given the phone number of the BC inspector for this area of Manchester, who I was to contact to arrange a pre-commencement visit.
The Building Control Inspector visited, and after a bit of small talk I told him that we had improved the sub-floor ventilation using telescopic vents, and airflow had been calculated and found adequate. He spotted a woodfibre batt in the corner of the room, said it looked to be at least 100mm thick (it was actually 120mm), and then said “as long as it’ll be better than it was before I’m happy”. And then he was off.
So after a bit of unccertainty, none of the u-values, sub-floor ventilation or payback period calculations were needed in the end.
So what was the point of all that? If you have future problems you certainly can’t be accused of failing to follow the Building Control Inspector’s advice.
After being party to some of your thoughts and concerns along the way I am more confident in your understanding of the issues than the Building Control Inspector’s.
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I’ve learnt something at least!