It should be noted that the heat loss models prepared in this exercise comply with BSEN12831 because this is the standard that is generally required for sizing heating systems in domestic dwellings, such as heat pumps and also the standard required for government grants such as the Boiler Upgrade Scheme. This is a fairly simplistic model as it does not account for building orientation, solar gains (heat through windows) or internal gains (heat provided by activities such as cooking and heat from humans and animals within the building)

It should also be noted that all houses are different and the insulation measures we look at in these examples may or may not be suitable for your property.

Only when you know the heat losses of your  home , can you look at ways of improving it. If you would like is to model your home, please get in touch.

Our example house is  a fairly typical mid 20C detached house, it’s 3 bedroomed with approximately 100m2 internal floor space, located in the midlands.

Construction wise, it had :-

• A suspended ground floor
• brick cavity walls
• a pitched roof
• single glazing
• Solid wood doors
• No insulation was used. Loft insulation in the UK wasn’t mandated until the late 1960’s .
• Open fires

When this house was built no insulation was used, so for this model we will be using the following u-values:-

• 1.20 W/m2k Suspended ground floor
• 1.60 W/m2k External Brick cavity walls
• 2.30 W/m2k Pitched roof no insulation
• 4.80 W/m2k Single glazed windows
• 3.00 W/m2k Solid wood doors

The house was not very air tight and so we have assumed air tightness would be around 15m3/hr:m2 at 50 pascals and because there were open fires in the lounge and dining room, air changes rates for those rooms is likely to have been 6.5 air changes per hour. 

So it comes as no great suprise that the heat losses for this version are very high.

Clearly this model is quite extreme but is representative of the few remaining buildings of this type.

Lets drill down in to the data

There are five rooms (shown in pink) which stand out as being exceptionally cold:-

Both the living room and dining room have open fires, so any heat in the room has an unimpeded escape route, straight up the chimney, this alone increases the air change rate by 5 air changes per hour.

The first floor rooms have a simple lath and plaster ceiling adjacent to the unheated and uninsulated lost space.  Additionally the bathroom is designed to be warmer than the adjacent rooms and so it will transmit heat to them.

Interestingly, you will note that both the hall and landing have relatively low heat losses. This is primarily because they are adjacent to warmer rooms, which allows heat to transfer into the hall and landing.

Following the advent of smokeless zones in the UK, much of the housing stock with open fires had these decommissioned.

By the 1970’s on the back of the global energy crisis, the UK government insentivised the installation of loft insulation.

In this example we have assumed

1) That our house no longer has open fires.

2) That our house has 50mm mineral wool insulation installed in the loft

No other changes were made

So for this model we will be using the following u-values:-

• 1.20 W/m2k Suspended ground floor
• 1.60 W/m2k External Brick cavity walls
• 0.68 W/m2k Pitched roof with 50mm inulation
• 4.80 W/m2k Single glazed windows
• 3.00 W/m2k Solid wood doors

The house was not very air tight and so we have assumed air tightness would be around 15m3/hr:m2 at 50 pascals
and because there are no longer any open fires in the lounge and dining room, air changes rates for those rooms is likely to have been reduced to 1.5 air changes per hour.

Even with these limited improvements the resulting reduction in the building heat loss not insignificant.

Dwellings with such limited insulation are quite rare but this model is is representative of the few remaining buildings of this type.

Lets drill down in to the data

So immediately visible are the reduced heat losses to both the living room and dining room due to removal of the open fires.

And whilst the level of loft insulation is significantly less than current standards, there is still a reduction to the heat losses of all first floor rooms.

The result of these simple improvements is a reduction of over 32% in the total heat load when compared with the original house

By the 1980’s double glazing became much more deployed in the UK

In this example we have assumed

1) That our house no longer has open fires.

2) That our house has 50mm mineral wool insulation installed in the loft

3) Double glazing was installed to the entire property

No other changes were made

So for this model we will be using the following u-values:-

• 1.20 W/m2k Suspended ground floor
• 1.60 W/m2k External Brick cavity walls
• 0.68 W/m2k Pitched roof with 50mm inulation
• 2.80 W/m2k Double glazed windows
• 2.80 W/m2k Double wood doors

The house is now a little more air tight and so we have assumed air tightness would be around 10m3/hr:m2 at 50 pascals

With these  improvements the resulting reduction in the building heat loss reduces further

This model is rather typical of older housing stock that have been in the same ownership for a number of years and have recently come onto the market requiring updating

Lets drill down in to the data

So immediately visible are the ground floor rooms, which are now showing fairly reasonable heat losses mainly due to the installation of double glazing (and remember new double glazing units perform significantly better than the 1980’s units we have used in this model.

First floor rooms have improved a bit but are still showing fairly high heat losses, (this is because we have still assumed low levels of loft insulation)

The result of these simple improvements is a reduction of around 13% in the total heat load compared with version 2 and over 40% reduction compared with version 1

By the 1990’s there was a drive to improve the insulation in older houses, this included enhanced loft insulation and retro installed cavity wall insulation

In this example we have assumed

1) That our house no longer has open fires.

2) That our house has 150mm mineral wool insulation installed in the loft

3) Double glazing was installed to the entire property

4) Cavity wall insulation has been installed

No other changes were made

So for this model we will be using the following u-values:-

• 1.20 W/m2k Suspended ground floor
• 0.70 W/m2k External Brick cavity walls
• 0.35 W/m2k Pitched roof with 150mm inulation
• 2.80 W/m2k Double glazed windows
• 2.80 W/m2k Double wood doors

The house is now a little more air tight and so we have assumed air tightness would be around 10m3/hr:m2 at 50 pascals

With these  improvements the resulting reduction in the building heat loss reduces further

This model is rather typical of older housing stock that have been in the same ownership for a number of years and have recently come onto the market requiring updating

Lets drill down in to the data

So immediately visible are the ground floor rooms, which are now showing fairly reasonable heat losses mainly due to the installation of double glazing (and remember new double glazing units perform significantly better than the 1980’s units we have used in this model.

First floor rooms have improved a bit but are still showing fairly high heat losses, (this is because we have still assumed low levels of loft insulation)

The result of these simple improvements is a reduction of around 25% in the total heat load compared with version 3 and over 56% reduction compared with version 1

Let’s assume that our house is now in new ownership and the current owner wants to improve the house to modern  standards

In this example we have assumed

1) That our house no longer has open fires.

2) That our house has 300 mm mineral wool insulation installed in the loft

3) New double glazing was installed to the entire property

4) Cavity wall insulation has been installed

5) the suspended floor has been insulated with 150mm PIR insulation (this may not be practical in all old houses)

6) The house has been air pressure tested and air leakage has been reduced to 5m3/hour, which also reduces the individual room air change rates

No other changes were made

So for this model we will be using the following u-values:-

• 0.18 W/m2k Suspended ground floor with 150mm PIR insulation
• 0.70 W/m2k External Brick cavity walls
• 0.13 W/m2k Pitched roof with 300mm inulation
• 1.40 W/m2k Double glazed windows
• 1.00 W/m2k Upgraded external  doors

With these  improvements the resulting reduction in the building heat loss reduces further

This model is rather typical of older housing stock that have been changed ownership recently with new owners upgrading the property

Lets drill down in to the data

around So immediately visible all rooms are performing significantly better than the previous versions, The improved insulation clearly helps, but also the improved airtightness of the building, significantly reduces the heat load.

We highly recommend home owners commission an air tightness test, as typically actual air tightness rates are better than assumed default values.

The result of these simple improvements is a reduction of around 44% in the total heat load compared with version 4 and around 75% reduction compared with version 1

Whilst all insulation improvements will reduce the heat your building requires ( and potentially reduce your running costs )  Some forms of insulation are more cost effective than others, and quite often as you move more and more to higher specification (better performing insultion) the capital costs versus running costs savings can reduce (diminishing returns).

It should also be noted that not all forms of insulation are suitable for all buildings. For example spray foam roof insulation can lead to problems with mortgage lenders.

(The Royal Institution of Chartered Surveyors (RICS) have produced an  impartial and comprehensive guide written by subject matter experts to update consumers on the latest guidance about the use of spray foam as a method of insulating residential properties.
(https://www.rics.org/news-insights/rics-release-new-spray-foam-consumer-guide)

If you commission us to prepare a heat loss calculation for you, we can then ammend the model for you to show you the impact of various different types and levels of insulation. Thus enebling you to make an informed decission as to which improvements work best for you.