In the fourth of the series of blog posts regarding retrofitting homes to be more sustainable, PJH are looking into insulation retrofit. Beginning with an introduction and brief history, comparisons with and without additional insulation and costs per m².
Insulation Retrofit Introduction
A basic yet fundamental part to a retrofit (with an eye on sustainability and energy efficiency) is minimising heat loss through the building envelope. This can be achieved by assessing where in the dwelling is most vulnerable; through visual assessment, smoke tests, thermal imaging and rectifying it through increasing air tightness and thermal performance. Retrofitting older housing stock can involve installing cavity wall insulation, replacing windows and doors and installing or improving loft (and suspended floor) insulation to increase energy efficiency. For new build or extension projects, owners have the added benefit of being able to choose insulation based on thermal mass, thermal conductivity, thickness and environmental implications, all in accordance with enhanced thermal properties to suit current building regulations. It is also important to try and choose a material that has a lower embodied energy due to the implications of importing carbon through the import of non-natural materials. However, this is not always an option due to the limitations of the existing housing stock and the type of wall construction that the property consists of. If you are wanting to retrofit your home with “eco-upgrades” for it to be more sustainable but are limited by the wall construction not having a cavity, consider the benefits of adding insulated plasterboard internally.
When discussing a dwelling’s thermal performance, U-value is referred to as the measure of a material’s performance, the closer a number is to 0 the better. U-value actually refers to the materials W/m2K (Watts-per- meter-square-kelvin).
U-Value Requirements – Historical up to Current Values
The table below shows the history of the u-value requirements for different components of a dwelling from when the first set of national building regulations was set out in 1965. As the years have passed and knowledge of thermal performance and the need for reducing a properties energy use has increased, the national u-value requirements have increased (closer to zero) also. The requirements have changed dramatically since the first set of building regulations came out, with 2022 updated figures requiring walls to have a u-value of at least 0.18 W/m2K. With the UK government’s goal of becoming net zero by 2050, providing greater efficiency in homes will be of greater significance.
Table showing history of U-value requirements for different building elements at different points through time since the introduction of building regulations.
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Floor Insulation Retrofit Comparison
The three most common floor construction methods in the UK are; ‘ground bearing concrete’, ‘suspended beam and block floor’ and ‘suspended timber floor’. In the following tables, it can be seen how the different P/A ratio can effect the level of insulation thicknesses required to achieve differing levels of U-values. The P/A ratio refers to the exposed perimeter of a ground floor divided by the floor area.
Table showing ground bearing concrete floor typical rigid board insulation thicknesses and representative u-value’s based on P/A ratio. Insulation values shown representative for use of Kingspan K103.
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Timber showing suspended beam and block floor typical rigid board insulation thicknesses and representative u-value’s based on P/A ratio. Insulation values shown representative for use of Kingspan K103.
Table showing suspended timber floor typical floor insulation slab thickness and representative u-value’s based on P/A ratio. Insulation values shown representative for use of Rockwool Flexi.
Wall Insulation Retrofit Comparison
An approximate calculation for the U-value of some of the most common types of wall construction for the existing stock in the UK can be seen below. Also included is the U-value after adding 32.5mm vs 52.5mm Kingspan K118 insulated plasterboard and how this can improve a dwelling’s thermal performance.
Table showing typical wall construction and U-value as standard and after the addition of insulation internally.
The following table shows how when the retrofit/renovation of a building element is undertaken, they must be upgraded to meet the improved u-value figures. This works off the provision that a building regulations application is submitted.
Table showing building elements and U-value’s required to be achieved when upgrading specific elements as per Approved Document L, as of 1st March 2023.
Roof Insulation Retrofit Comparison
Below are two tables showing how the two most common types of pitched roof construction methods (warm vs cold) can be retrofitted in order to achieve different U-value figures based on differing levels of insulation. When the space within a pitched roof is used as habitable spaces, rigid board insulation is found between and over the rafters which is referred to as a ‘warm roof’. A cold roof is when the insulation sits between and over the ceiling joists leaving the pitched roof void above cold and inhabitable.
Table showing warm roof insulation and u-value comparisons.
Table showing cold roof insulation and u-value comparisons.
Costs – per m²
Based on the examples above, potential products for each can be seen below with the average costs per m². (Prices based on information from Insulation Superstore prices as of 1st March 2023)
Kingspan K118 32.5mm insulated plasterboard cost per m² = £25
Kingspan K118 52.5mm insulated plasterboard cost per m² = £32
Kingspan K107 50mm pitched roof rigid board cost per m² = £22.62
Kingspan K103 100mm floor insulation board cost per m² = £43.15
Rockwool Thermal Insulation roll 200mm cost per m² = £21.51
Conclusion
In conclusion, there are many benefits to increasing insulation within your existing dwelling as part of a retrofit or extension. The increased performance of a property’s envelope will reduce heat loss, aid in the reduction of monthly running costs and be easier to maintain a comfortable environment. The above examples of different wall, roof and floor constructions show how even older properties can benefit from an insulation retrofit and reduce the carbon footprint. Further information on Approved Document L and the building regulations discussed in this blog can be found on the GOV.UK website here.
Ask us for advice
If you have a project in its infancy and want to have an informal chat regarding your options, feel free to contact us, we are always happy to provide friendly and knowledgeable advice. Get in touch on 0161 460 0382 or email the team at enquiry@pjhas.co.uk
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