Installing Underfloor Insulation (Ground Floor)

LUHG1878

Hi,

We moved into our home almost 2 years ago, and last year it cost a fortune to heat over the winter. I believe there were a couple of reasons for this, poorly fitted double glazing by the previous owner, and zero insulation.

The house itself is a 1920's bungalow, solid brick construction with no cavity.

We had the loft insulated & floored during the summer, and we're in the process of having new double glazing fitted, so that should make a big difference.

The next area I want to tackle is under the floor. Rooms to the front of the house have suspended timber floors, those to the back have basement rooms below.

It's the rooms to the front I want to concentrate on, they have a concrete base, wooden joists, floorboards, with air bricks at the front of the house. The void between the concrete base and the underside of the floorboard is approx 250mm high. The distance between the joists is approx 410mm.

1) Should I put down a damp proofing membrane of some sort on the concrete base and, if so, any suggestions?

2) What type of insulation would be best for this job?

3) To what depth should the installation be fitted? (thinking I would still need to leave space for the air to circulate?)

4) Should a vapour barrier be fitted on top of the insulation before the floorboards go back down?

I'd really appreciate any comments/suggestions as this is something i'd like to tackle myself.

Thanks

huckster

Think you would need to have an inspection done by someone who deals with this, so they can recommend the best solution for your house.

kiddakidda

LUHG1878 wrote: »

Hi,

We moved into our home almost 2 years ago, and last year it cost a fortune to heat over the winter. I believe there were a couple of reasons for this, poorly fitted double glazing by the previous owner, and zero insulation.

The house itself is a 1920's bungalow, solid brick construction with no cavity.

We had the loft insulated & floored during the summer, and we're in the process of having new double glazing fitted, so that should make a big difference.

The next area I want to tackle is under the floor. Rooms to the front of the house have suspended timber floors, those to the back have basement rooms below.

It's the rooms to the front I want to concentrate on, they have a concrete base, wooden joists, floorboards, with air bricks at the front of the house. The void between the concrete base and the underside of the floorboard is approx 250mm high. The distance between the joists is approx 410mm.

1) Should I put down a damp proofing membrane of some sort on the concrete base and, if so, any suggestions?

2) What type of insulation would be best for this job?

3) To what depth should the installation be fitted? (thinking I would still need to leave space for the air to circulate?)

4) Should a vapour barrier be fitted on top of the insulation before the floorboards go back down?

I'd really appreciate any comments/suggestions as this is something i'd like to tackle myself.

Thanks

One of the biggest differences I made in my house (Victorian 1900 - double solid brick - no cavity) was to batten the interior walls by about an inch, insulate with 25mm celotex / polystyrene type board, plasterboard and skim.

You will still lose heat but it has made a big difference.

The other thing on older houses is seeking out draughts, I have been seeking for years a trying to block at source but yet to find the holy grail and cut out all draughts.

Watch out for condensation though

good luck:beer:

zzzLazyDaisy

You need to address heat loss through the walls, as this is the largest area of heat loss. You can get thermal plasterboard which makes insulating solid walls easier. It is not cheap, but if you do each room as you decorate the house your can spread the cost.

Leon_W

Agree with the above.


Your money would be better spent internally insulating all the external walls.

DRP

From a money saving perspective I would wait til after the winter. The cost of underfloor or wall insulation will never be returned by potential fuel savings.

You've insulated loft and just installed double glazing, these may make all the difference.

I was in similar house and the top 3 changes were:
Double glazed window
Composite door
Adequate radiators (£ for £ the best investment)

We also insulated the suspended floor with Celotex, but the improvement was incremental at best compared to the list above.

LUHG1878

Hi All,

Thanks for the replies, very much appreciated!

Insulating the walls is a great suggestion, something I hadn't considered, as I knew there wasn't a cavity to fill, and insulating externally would cost too much, but fitting thermal plasterboard to external facing walls as we're decorating is something we'll definitely do. I've had a quick look and boards range from 22mm to 40mm thick and for a 2.88m2 board you'd be looking at between £15-20. (Gyproc ThermaLine Basic)

We've also been replacing radiators throughout the house as we've been decorating the rooms, so only a couple more to go, and it does make a difference, as has been commented.

I do still intent to insulate under the floor though, as reducing or eliminating these draughts will make a big difference, particularly in the living room where we just have the wooden floor. (no carpet)

I think i'm going to go with 50mm Celotex, it's pretty easy to fit by all accounts, and only about £20 per 2.88m2, so it won't be a major expense per room.

I've also learned that there's no need for a damp proofing membrane, or vapour barrier, just a case of lifting the floorboards, fit the Celotex so that it's level with the top of the joist, and tape along all joints and edges with tape to ensure all the gaps are sealed. It's then just a case of putting the floorboards back down.