Air tightness/insulation bungalow retrofit

[oliviaaa999]

Hi all! We're currently working on a 60's bungalow that we're planning on adding MVHR to, but we're a bit confused about the next steps. We're looking to improve airtightness but can only do so much with a limited budget. The current plan is to eventually insulate the suspended cavity from beneath once we've moved in, but we're not sure whether to have an airtight membrane be above or below the floorboards? We're looking at simply screwing plywood to the existing floorboards and airtight-taping those, as well as sealing around any pipes/sockets. Then having the airtight membrane end at the ceiling (not including the loft for simplicities sake as we don't intend on extending upwards). My concern is whether this is at all correct as further reading leads down the path of cavity walls being awful for airtightness, but I have no idea how we could fix that. 

 

The floorboards are currently bare and the skirting is all off with the walls and ceilings being skimmed, so I'm hoping now is a good time to work on the airtightness, so if anyone has any steps they followed to retrofit airtightness (especially on a minimal budget) I'd be very grateful! Especially advice on products/methods to use.

[jayc89]

Windtightness on the cold side of the insulation, airtightness on the warm side. 

 

For a suspended timber floor, I'd do this - https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors

[MikeGrahamT21]

Have a look at my blog, as i'm doing the same kinda stuff, might be helpful for you: 

 

[IGP]

On 07/04/2024 at 20:26, jayc89 said:

Windtightness on the cold side of the insulation, airtightness on the warm side. 

 

For a suspended timber floor, I'd do this - https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors

I did this, got a lovely warm floor!

 

Things to reflect on - I went mineral wool over the hemp they specified and used the Pro-Clima membranes and tapes etc. The Pro-Clima membranes are amazing, but they’re a bit over-kill for the application in my opinion looking back. Get standard breather membrane (windtightness) and vapour membranes (airtightness) and you’ll be fine. However the Pro-clima tapes and membranes were worth the money and I’d highly recommend them regardless. 
 

 

[Sparrowhawk]

@IGP that looks excellent! And thanks for sharing your experience, as I've been eyeing up their method too.

 

How deep are your joists and the void underneath, and what U-value have you aimed for?

[IGP]

Thanks!

 

I’ve got 180mm joist depth which comes out about 0.2 u value. The void was probably about another 80-90cm to the ground below from the bottom of the joists. 
 

it’s just nice in winter when you can walk barefoot and not feel freezing on your feet. 
 

 

[Sparrowhawk]

You're so lucky with that joist depth. My entire joist + void depth is around 200mm.