Insulation – floors

When sitting on the sofa on windy days we could feel a draught blowing between our toes.

It’s essential to maintain airflow under floorboards so the joists don’t rot, so there are air bricks in the walls just below floor level to let the wind in. Problem is, that means the underside of the floor is cold, and the wind blows through any gaps, and around the edge behind the skirting boards.

A previous owner had taped up some gaps between the floorboards with parcel tape, which I suppose should work under carpets, but if your floorboards are exposed there are specific products available.

As I was sanding the floor I used the Old Pine Slivers

How to

If you can get underneath the floor you can insulate from below, stuffing flexible insulation between the joists and holding it up with netting. But no such luck in our case, that would be too easy.

So I took a crowbar to the floor and prised up the floorboards. With the floor removed I laid plastic sheeting over the joists to completely draft proof the floor. Care must be taken not to block the air bricks.

The sheeting forms hammocks between the joists into which I poured loose fill recycled newspaper insulation. Don’t worry, it’s treated to make it fire & rodent proof. Above the whole lot I placed a 2nd plastic sheet before replacing the floorboards. The 2nd sheet, directly underneath the floorboards, is to prevent moisture from the room absorbing into the insulation. Or spilt drinks for that matter. The prospect of smelling stale beer for weeks after a party does not appeal.

 

Under Floor Insulation

Product Warmcel – loose fill insulation made from recycled newspaper
Rating λ=0.040, 200mm deep
U-Value 0.2
Cost £2.50 per square meter at 100mm thick
£5 per 8kg bag
£140 for 2 rooms + £70 for plastic sheeting
Payback time about 4 years
Supplier Natural Insulations
Plastic sheeting from B&Q, sold as Damp Proof Membrane
(thicker gauge is much more difficult to work with).

 

Front room almost destroyed.  erm, I mean ready for under floor and wall insulation.
Front room almost destroyed. erm, I mean ready for under floor and wall insulation.

 

Air bricks provide essential airflow to the underside of the floor to prevent the joists rotting.  But it means the floor is cold and draughty.
Air bricks provide essential airflow to the underside of the floor to prevent the joists rotting. But it means the floor is cold and draughty.
I placed a piece of wood infront of the air bricks to ensure a clear space for air flow when the plastic sheet goes down around it.
I placed a piece of wood infront of the air bricks to ensure a clear space for air flow when the plastic sheet goes down around it.
Ready to begin.  But wait... the pipes supplying the radiator were on the cold side of the floor, but were not insulated.  Right, quick trip to the diy store for some pipe lagging, and then we're ready.
Ready to begin. But wait… the pipes supplying the radiator are on the cold side of the floor, but were not insulated. Right, quick trip to the diy store for some pipe lagging, and then we’re ready.
Plastic sheeting was laid over the floor joists and filled with Warmcel.
Plastic sheeting was laid over the floor joists and filled with Warmcel.
A second plastic sheet is laid over the top of the insulation (moisture and spill barrier) and the floorboards re-fixed.  The plastic sheeting sticking up around the edge was taped the walls for air tightness, and finally the skirting board replaced.
A second plastic sheet is laid over the top of the insulation (moisture and spill barrier) and the floorboards re-fixed. The plastic sheeting sticking up around the edge was taped the walls for air tightness, and finally the skirting board replaced.
The cold and draughty floor is now warm and air-tight.
The floor is now warm and air-tight.

 

Top Tip

Sawdust mixed with PVA adhesive makes excellent wood filler. I kept some sawdust from sanding the floors and used it to fill holes and seal under the skirting boards etc.

Replacement Floorboards

Inevitably, when lifting securely fixed floorboards some boards are damaged beyond repair. I found a couple of local suppliers for replacement boards who would exactly copy my sample of tongue and groove floorboard.

From reclaimed pine: Reclaimedfloorboardsuk

From new pine: Soper Group

Although the new pine boards were paler, staining with tea proved to be surprisingly effective.