Crawl space insulation

[Lord Frederick III]

Hi,

We purchased part of a mansion built in 1801 which has, until recently, been costing a fortune to heat. We've done as much insulation as possible (loft, double glazing etc), which has resulted in significant savings and all that is left now is to insulate the crawl space under the lounge.

The lounge is approx 8m2 with a parquet floor. The air vents push air into the crawl space, and this air then can be felt rising through the parquet flooring. Fine in summer, but not so ideal in winter. There are four options available:

• Do nothing and keep the heating on high

• Get rid of parquet floor by adding themal underlay and carpet over

• Add under floor heating. Not ideal for solid wood floors

• Keep parquet flooring and insulate under floor using Kingspan or equivalent

The later is the preferred option, although the other half would prefer a carpeted floor. The only issue with insulating is that the air vents are just below the floor. So if we were to insualte, the air vents would either get blocked by the insulation or still vent between the insulation and floor (they are big vents). Ideally the air vents need to ventilate under the new insulation which may be possible by using a duct to redirect the air flow under the insulation. We don't want to block the air vents as they have kept the crawl space and cellar dry. We are concerned that by insulating in the crawl space that we may introduce thermal bridging and all the associated problems with it.

Does anyone know of the recommended approach when it comes to period properties and crawl space insualtion? Happy to take recommendations for insualtion specialists in the Yorkshire area.

 

[DJH]

Welcome aboard my lord...I'm puzzled that parquet flooring, which by it's nature , is composed of tight fitting small pieces of wood generally laid on asphalt or similar, but on a timber floor? If there is draft coming up through then there must be gaps in the substrate and in the parquet too.

Maybe carpets or mats judiciously placed would be the less expensive option while maintaining good ventilation to the void below the floor.

Doug

 

[Flyfisher]

What about simply blocking up the air vents during the winter months? Any underfloor accumulation of moisture during those 4/5 months would surely dry out during the 7/8 warmer months and therefore not create a long term problem.

Just guessing though.

 

[agbagb]

I've found rockwool between the joist, held up and draught proofed with stapled up breathable roofing membrane (sarking) works well. It insulates and draught proofs whilst remaining breathable to avoid condensation build up. The rockwool and membrane can be shaped and stapled up higher where needed so the airbricks aren't blocked.

 

[MatthewC]

Whatever you do, do not permanently block off the ventilation of the space under the floor - and make sure that there are at least two holes to allow a draught to ventilate.

 

[renov8r]

Depending on the depth of your crawl space, and willingness to lift the parquet floor, I would also suggest the following as possible options:

Assuming no lifting of the parquet & a deep crawl space - you can cut a diffusion open vapour check into strips wider than the space between joists and staple and glue them to the joists immediately under the floor to create the airtight layer. Ensure no leaks around the perimeter or via any service cavities also. Then friction fit insulation under the vapour check to the depth of the joist, or deeper if shallow joists. Wool or hemp would be good materials in this case as they are breathable and you will be fitting them overhead in a tight space. Then install a breathable membrane, making sure to tape the overlaps and glue to walls. If you need additional physical support of the insulation, you can also staple chicken wire to the underside.

Assuming lifting the parquet - you can drape breathable membrane over the exposed joists to create a "tray" to the depth of insulation you want to achieve. Staple the membrane into the joists for support and tape/glue as above. Then fit the breathable vapour check, ensuring airtightness across the entire layer before finishing with the floor structure. An alternative to the breathable layer is to tape and seal fibreboard sheets on to the joists, but not all of these products are breathable.

Be careful using Kingspan in situations like this as depending on the subfloor, there may be considerable moisture rising, which when blocked by the Kingspan layer will be entirely absorbed by the only remaining exposed wood, i.e. the floor joists.

Example of vapour check (no affiliation): http://www.thegreenbuildingsite.co....-membranes/intello-plus-30m²-pcip20-pro-clima Make sure to check with the suppliers that their products can be used in such situations.