Insulation Retrofitting in Passive Homes

The most important word to use in an energy retrofit has to be insulate insulate insulate.

It is by far the best value for money in any renovation programme.

Retrofitting will involve choices and the best advice regarding insulation is given below.

An existing house can easily accept insulation to walls and attics and not so readily to floors. Walls

External wall insulation.

This is provided by a range of suppliers and contractors.

The external insulation market is dominated by plaster or render manufacturers and in many instances the insulation is secondary to the sale of the plastering product.

In brief the use of the external insulation systems is purely to sell plastering products.

The use of product certification is designed to ensure the quality of the system but has the effect of restricting the market especially in terms of grants.

The funny thing is that a bricklayer can install insulation badly in cavity walls and the wall will be certified to a U value but external insulation can only be used if it has a BRE certificate or an Agreement certificate.

1. Find out what type of insulation you are getting and its thermal conductivity. The poorer the insulation type the worse the reduction in wall U values.

2. Find out independently what reduction will it have on your walls U value.

3. Ask how windows will be treated.

4. Get a thermal image done before and after the plastering.

5. Get a breakdown of the price in particular the cost of the insulation per m2.

Whereas I am a keen advocate of external insulations the material costs are very expensive and the use of cheap insulation materials result in large thicknesses to achieve reasonable U values.

In many cases a reputable plastering contractor will install an external insulated plastering system for less than the cost of a propriety system with a grant.

If you are getting external insulation system installed look at the possibility of replacing your windows .

If replacing windows is outside your budget consider breaking out around them and installing insulated cavity closers.

This will improve your thermal breaks and ensure less heat loss

When using external plastering remove old concrete window sills and replace with pressed sills.

Internal Insulation

Internal insulation has many advantages in that having the insulation internally ensure a faster heat response time.

It is a messy solution and should only be considered if the house can be vacated or if sections of the house can be vacated.

Again the important items are treatment of windows and reducing cold bridging.

If you are considering internal insulations make sure you use the opportunity to air seal your house.

Sealing materials can be used and are covered by the insulation and plaster board.

In particular areas around windows can be treated for air tightness.

Dry lining or dry walling is probably the preferred option but if possible wet plastering will give a better finish and air seal.

This is the most popular system in retrofitting as it’s cheap and not envasive to the home.

The choice of material is important.

Cavity beads are the most common type of cavity insulation.It works fine in most cases but if cavity wall insulation is poorly fitted it may not fill the whole cavity.

This results in thermal looping and poor U value reductions.It will not air seal the cavity.

Water based expandable insulations have the advantage of forcibably filling the cavity thus making it airtight.

Both systems are reasonable in improving U values but the expandable foams offer a more certain cavity fill and can improve sound ratings.

Whichever system is chosen it will have only a marginal effect on the walls U value but will reduce air leaks which in itself can save a large percentage of heat losses.

Timber Frame Houses

Timber Frame houses have their cavity ventilated so cavity filling is not an option.

External plastering is an option but the cavity ventilation should be maintained.

Internal insulation is an option and will go a long way in reducing thermal bridging which are a feature of timber frame houses.

If you can renovate internally using an expandable foam instead of rockwool you will achieve a much better airtightness.

Attics

Retrofitting attics can substantially reduce U values in the roof area.By increasing the thickness of insulation over the roof joists it’s takes out the problem of thermal bridging.

The problem with increasing the thickness of insulation in the attic place reduces the mobility within the attic area and access to water tanks etc need to be addressed.

The other option is to spray the underside of the slate or tile and turn the roof into a warm roof.

Warm roofs are very popular when using the attic area for living or working areas.

It is advisable to place a vapour barrier on the warm side of the insulation to ensure no moisture penetration into the insulation.

Floors

Insulating floors is the most difficult part of refits.

If a floor is concrete the use of insulation is limited if possible at all.

Using a timber floor with a insulating blanket will help or using carpets will help.

If the floor is suspended insulation such as sprayed insulation, rockwool or phenolics can be used.

The main issue with suspended is to make it airtight.

As with the walls roofs and attics good insulation practises are intertwined with air tightness.

Retrofitting air tightness is discussed elsewhere.

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