insulation under wooden floorboards

[Lee66]

Hi, I have ripped up the carpets in the 1960s bungalow we are refurbing ready to alter pipework to radiators. the floorboards look in great condition with no gaps with exception of edges where I removed skirting boards. I dont need to lift many boards to alter pipes but am wondering while i,m at this stage would there be a significant benefit in lifting them all and insulating between floor joists. this is by no means going to be an airtight place but as heating costs rise will the benefit out way the cost and if so what insulation will suffice. thanks

[Temp]

The void under a timber floor should be ventilated so yes to insulation. Both floor and pipe.

[MikeGrahamT21]

Take a look at my blog to see how i've done it, i'm also in a 60s bungalow. I've used PIR, but always make sure that there is something holding the PIR in place from underneath, i used metal clips screwed into the joists, as I have had it in the past drop down with the natural movement of walking on the floors. Plenty of expanding foam in any gaps, and whilst the floorboards are up you may as well whack an airtight membrane down before putting the boards back in, even a breather membrane will be better than nothing if you don't want the expense, and make sure its all taped up and taped to the wall before skirting goes back on.

 

Make sure all ventilation paths are fully open, and insulate the pipe as temp has said, as the temperatures following insulation to the floor in the void will be much colder during winter than before.

[TonyT]

What’s the depth under the floor?

maybe you can crawl under?

I used 100mm of rock wool slab friction fit.

 

[tonyshouse]

Work ough to comply with building regulation minimum standard but it would be better to insulate to o much better standard. Fully agree with making homes airtight 

[Marvin]

Where I live I insulated my approximately 105m2 floor with 2 layers of 100mm PIR board, one in between my floor joists, and one across under my floor joists by using long screws and batten. It was only worth doing that much because the walls and roof have similar insulation.  Whilst under the floor has some protection from the cold I save approximately 10kw per hour if I want 23C inside and its 0 degrees outside just from the floor insulation. 

 

I have LPG which is supplied in 47kg bottles so I know exactly how much energy I use on hot water and heating, and the last 12 month review meant I used about 6000kW hours for the whole year. Often people talk about what in theory they would use, using this, and that, but I know coz I counted the bottles that woz empty!

 

I have also insulated an existing bungalow floor by lifting up the carpet and making a hole in the floor to slide strips of insulation and batten in. That also had an incredible effect.

 

The rule of thumb for me is if your going to stay in your property (not doing up to sell) then definitely insulate a suspended timber floor if there is enough depth.  (and foam any gaps to keep the joists snug).

 

So if I was doing one layer of 100mm at about what £20 per m2?  So for the one layer I would by about £1,900 of board for 105m2 floor (don't forget to deduct for the width of the timber joists if its going in between) Batten and screws say £100 so budget 2k. It would take me about 3 weeks to install going under the floor and avoiding cables. 

 

For a suspended floor of 100m2 with no insulation ( floorboards and carpet between you and the cold air) when it was a constant 5C outside and a constant 23C inside (this never happens!)  I estimate you would be losing about 10.39kW per hour through the floor. 

For a suspended floor of 100m2 with 100 rigid insulation between joists when it was 5C outside and 23C inside  I estimate you would be losing about 0.431kW per hour through the floor.  Saving about 240kW a day in these conditions.

 

Well, someone is sure to correct me, but that's what I roughly calculate.