Our large five-bed detached home was built in 1978 and eight years ago we replaced our windows (and front door, etc) with triple-glazing and wrapped the walls of the house externally at the same time. The attic insulation and venting were also brought up to the standards then applying.
Since then, we've been informally advised that the BER rating is likely to be a C1 or so.
However, we never did anything about insulating below the raised wooden ground floor. It didn’t come up for consideration at the time. Recently, we started to consider this in the context of replacing our carpet in the lounge/dining room with laminate flooring.
We did some research on Google and contacted an insulation firm which offers a service whereby they pump a “breathable” insulation material into the underfloor void. It also provides cavity wall and attic insulation, using a similar process, we believe.
We contacted the Sustainable Energy Authority of Ireland (SEAI) about this but were merely advised this form of insulation is not grant-aided. They referred me to the National Standards Authority (NSA), but after this I’m none the wiser.
Can you advise if it is likely to be appropriate for an insulation substance to be pumped via vents into the plinths of our house (five, with three in front).
I'm aware of another insulation option for floors like ours but we haven't yet pursued this due to the likely high cost and inconvenience involved in taking up all the floorboards etc.
Fergus Merriman writes: This is a great question and with energy costs rising so quickly it's good to hear that you have already taken steps to reduce your energy needs with an external wall insulation system wrap. As you have ticked off items on your list, the remaining areas have begun to show up, so your uninsulated floor appears relatively colder than it once might have appeared and so has become your focus for attention.
Houses in the 1970s and 1980s were mainly built with solid floors. Only since the introduction of building regulations in the mid-1990s have they had any form of insulation. Solid floors are very hard to retrofit so you are lucky in having suspended ground floors which is an area often overlooked for insulation upgrades.
In suspended floors, air is allowed into the subfloor via vents so that the timber joists are kept in good health. Unfortunately, this cold air also cools the floor and infiltrates the house through the inevitable gaps, to further reduce energy efficiency. The introduction of insulation is relatively simple but the potential for failure of the vulnerable timbers becomes the big issue that is hard to overcome unless the correct approach is taken. Hence the reluctance for the SEAI to grant aid such intervention. It seems so simple just to pump in some form of insulating material – so what is the mechanism for failure that must be avoided?
First, the “suspended” timbers must be kept off the damp ground and separated with damp-proof materials at supports. Filling the gap with the wrong insulating material bridges the space allowing dampness to seep up and contact the timbers.
Second, the blocking of ventilation makes the potential for rot in the now warm wet timbers a huge risk.
Third, the potential for condensation to occur below the floor in newly installed insulation can work against energy efficiency and worsen the first two problems.
Then there is another potential problem which is bridging damp-proof courses with material that can “wick” up water and make the walls damp too, all of which explains why so many houses are built with solid floors albeit with insulation later included and why insulating below suspended floors is so often overlooked or considered too problematic.
The solution appears simply to lift the floorboards and slot insulation between the joists. However this can lead to the issues noted unless critical items are considered, including thermal performance, airtightness and condensation and moisture control. First, you must assess the condition of the subfloor zone before deciding on how these three things can best be resolved. This means inspecting below the floor, assessing if “oversite concrete” exists, the state of the timbers and the locations of the damp-proof courses. Once this is done then an insulating approach can be decided upon.
However, to be absolutely sure, the big step that must be taken is to lift the floorboards. The next steps, all of which must be carried out meticulously, are;
– fitting a breathable membrane below, or tightly fitted around the joists (noting the difficulty at supports and junctions);
– inserting high-quality insulation material;
– overlaying with a fully sealed vapour barrier including lapping behind skirtings; and
– carefully relaying the floorboards.
The work will be costly and disruptive, and even then there will be some junctions which cannot be fully resolved and may cause future issues.
Recently, new products have entered the Irish market using recycled glass waste made into foamed insulation granules which overcome most of the potential downsides to insulating these spaces because these materials do not wick water by capillary action, they allow some extent of breathability, reduce air infiltration, and allow any condensation to drain away while bringing the timber into the internal warm zone.
These can be pumped into subfloor spaces with a degree of certainty or poured in through uplifted floorboards. While these materials have been used in Europe for many years, they are not yet assured for use here in Irish conditions, but I am watching to see how certification progresses as they will resolve many cold floor problems in homes.
Fergus Merriman is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie
