Introduction
Let's face facts, insulation is the boring great-uncle of the sustainability family. Other aspects of sustainability feel more active, more dynamic, closer to the technological bleeding edge – "I've fitted solar panels with battery storage", "I've changed my car for an electric vehicle”, and so on – but make no mistake, boring insulation is one of the most significant contributions you can make to both sustainability and economy. Remember that a very significant proportion of your carbon footprint is due to heating.
Starting with insulation is called a “fabric first” approach to sustainability. As the saying goes, it's easier to save a pound than earn a pound - and that's true whether you're talking about a pound's value spent on energy bills or a pound's weight of emitted carbon. The savings compared to the outlay for stopping energy losses are staggering compared to the equivalent savings for generating your own energy.
Our unenviable task in this month's Sustainability Pathway is to make insulation sound relevant and appealing. We've timed this topic so that you've got a chance to consider your options before the weather turns colder.
In this topic...
What can be insulated?
This graphic illustrates where energy escapes from a typical house:
While the percentage will vary between different styles and ages of houses and flats, the exit points are the same. In this study we consider how you can insulate the roof, windows, walls and floor of hour house, and also consider pipes and tanks, as well as tackling draughty gaps.
Issues with insulation
You’ll hear suppliers boasting about the “R” and “U” values of their products. Simply put:
· R values measure the ability of a material to resist heat – higher numbers indicate better insulation.
· U values measure the ability of a material to transmit heat – lower numbers indicate better insulation.
These figures help the heat losses from different parts of a building to be compared. For example:
Material | Typical U-value (in W/m2K) |
Single glazing | 4.8 – 5.8 |
Double glazing | 2.1 – 2.8 |
Triple glazing | 0.8 – 1.7 |
Solid brick wall (typical 228mm thick) | 2.1 |
Cavity wall with no insulation | 1.37 |
Cavity wall with 50mm insulation | 0.56 |
Uninsulated roof | ~2.5 |
Loft with 270mm of insulation | 0.15 |
Solid timber door | 3 |
Insulation done incorrectly can cause condensation. Warm air can carry more water than cooler air – that's why when warm, moist air hits a cold window it loses some of that moisture as visible condensation on the window. In the developed world, we've become adept at making the air in our homes quite moist by cooking, showering, drying clothes and breathing! If insulation is going to start making some areas of your house colder (e.g. wall cavities, roof voids) then condensation can occur there – so either the damp air should be prevented from getting there (e.g. fitting a plastic sheet as a "vapour barrier" over the insulation) or there should be a mechanism for safely removing the moisture (e.g. drain holes or vents).
Note that when people talk about "insulation" this could either mean thermal or acoustic insulation. In many cases a material that limits the travel of heat also limits the travel of sound (a double win!) but this is not always the case.
Windows
There are some worthwhile interim improvement measures that don’t require total replacement of windows:
secondary glazing consists of a separate second set of windows which sit inside the existing window bays – typically these open with a sliding mechanism. As well as being cheaper than fitting double glazing, this can be a useful solution where listed building status or similar restrictions prevent a change in the appearance or construction of the existing windows.
window film (as loved by frugal students in rented properties!) is a cheap and easy way of making a useful improvement to sustainability – although you don’t be able to open the windows afterwards. Attach the film to the window frames with the double-sided tape provided, then warm it with a hairdryer until it goes tight!
double glazing fitted in the 1980-90s may now be well behind the performance can be achieved with modern materials, and the seals and fittings that keep our draughts might have worn. In some cases existing double glazing can be serviced or upgraded rather than completely replaced.
If you are considering window replacement, it’s sad to discover that a lot of glazing companies will offer a handful of types of glass and claim this is a wonderful selection. This might be the limit of their knowledge or it might simplify stock management in their workshops, but the real selection of possibilities is far broader.
Leaving aesthetics (patterned, tinted or frosted glass) aside, modern glasses can be designed for:
Heat retention (to stop heat leaving via the windows)
Heat reflection (to prevent sunlight from overheating a room)
Ultra-violet light protection (e.g. to prevent fabric colours fading due to sunlight and to help people with UV-sensitive conditions)
Noise reduction (sometimes using a near-invisible rubbery layer sandwiched between two pieces of glass)
Self-cleaning (an external coating that helps rainfall wash the dirt off – very useful for hard-to-get-to windows such as conservatory ceilings!)
Security (e.g. laminated windows which might crack but do not shatter if someone tried to break them)
Safety (e.g. glass in certain windows must be either laminated or toughened to prevent injury from large shards of glass if an over-energetic younger person were to crash into it!)
Choosing the right glass can therefore create a safety and security upgrade as well as a sustainability enhancement! Note that the glass is only one part of a window – the frame materials and construction (gaps etc) also contribute massively to thermal performance. Triple glazing is becoming increasingly common.
For anyone who wants to learn more, Pilkington Glass have a superb online tool for specifying glass called "Spectrum" (https://spectrum.pilkington.com/) - it's free to use after a simple registration. It's a bit technical (really intended for architects and engineers!) but can be an engaging way of learning what combinations of glasses, coatings, gaps and fillings make a difference! If you are looking at getting replacement windows, it can be used to produce a code that can be specified to your glazier so they can order in the glass of your dreams.
Don't be afraid of pushing tradespeople to consider a different type of product to what they have previously offered – If they're any good they will treat it as a learning experience, and in many cases will add it to the handful of options they offer to other clients – helping those clients to also be more sustainable!
Walls
Since the mid-20th century, most buildings in the UK have been built with cavity walls - these consist of an outer skin of brickwork (what you see) then a gap, then an inner skin of breeze block which can be plastered and painted. The air in the gap reduces heat transfer out of the building and damp transfer into the building. Practices changed in the 19x0's to put sheets of insulation into the gap to further reduce heat transfer. It also became popular to inject insulating material into the gap of original uninsulated cavity walls by drilling access holes into the outside - this improved the thermal efficiency of the walls. Unfortunately a lot of this work was done carelessly and left houses with patchy insulation or damp problems.
If you don't have cavity walls (before mid-20th Century – the pattern ("bond") of the brickwork can also give clues!) any insulation has to be added to either the inside or outside of the wall.
Internal insulation involves building an insulated from on the existing wall surface, then filling this frame with slabs of insulation, then putting a plasterboard wall on the inside and decorating it. Clearly, doing this will make your rooms slightly smaller by about 10-12 cm for each wall treated, and the room will need to be redecorated afterwards. However, this can be done on a room-by-room basis and so can be combined with other planned redecoration activities.
(An example of internal wall insulation before the vapour barrier and plasterboard is fitted)
External insulation involves attaching slabs of insulation to the outside of walls and then covering this (e.g. with render, thin brick/stone "slips" or wooden panelling.) This has far less internal impact, but can't be done a room at a time. It makes the outside of the house bigger, and changes its appearance – this can be advantageous if you needed to redecorate anyway, or may be a major obstacle for a property with existing external character.
Once upon a time, people would make a marginal improvement to a wall's thermal performance by adding an internal layer of polystyrene, and then covering it with wallpaper or a wooden veneer. The modern, far more effective (and thankfully more fire-retardant!) equivalent of this is to use a thin layer of Aerogel (see http://www.aerogel.uk.com/). This is a relatively new wonder-material that gives effective insulation from a thin layer but is still little-known in the building industry and slightly awkward to handle, so not widely used yet. The materials typically cost five time what an equivalent thickness of conventional insulation would cost, but only required a third of the space – so it’s best used where space is at a premium.
There are specialist paints with particles in that form a thermally insulating layer on a wall, but the effect is marginal compared to other forms of insulation, the cost is high and line all painted surfaces, you have to repaint them far more often than you’d have to replace regular insulation. We’re not certain that we could recommend this for most situations.
Improvements to wall energy efficiency can also be made by:
“parging” an internal wall (painting on a thin cement layer which stops up any cracks) to reduce air leakage. This is usually done before fitting internal wall insulation.
repointing external faces of walls to prevent water ingress – the heat required to make that water evaporate is coming from your property so less water means less lost heat! The use of paint-on waterproof coatings is contentious as it can trap water inside a wall leading to damp problems.
Remember that in a well-insulated buildings, it's possible for a room to get too hot instead of too cold, and as our climate changes, this will become a more significant consideration. Make sure that there is a way of cooling a well-insulated room (e.g. an opening window) for those few extreme days in summer!
Pitched (sloping) roofs
The best known type of insulation is the rolls of glass fibre installed in lofts under pitched roofs; it's also simple to install and very effective.
As with other forms of insulation, standards have changed over time, and a loft insulated 20+ years ago will be significantly short of the modern recommended depth of 270mm giving a U-value of 0.15 W/m2K. As the recommended thickness is now higher than the depth of the ceiling joists that the insulation fits between, it’s common to insulate with one layer up to the top of the joists, and then add a top layer at right angles to the joists to get to the recommended depth.
The usual warnings when insulating lofts:
Wear gloves and a mask – the fibres which form the insulation are small and sharp, and you don’t want these in your hands of your lungs. Some types of insulation are now available in a plastic wrap which stays in place after fitting, which helps this issue .
When insulating the edges of the loft, don't cover ventilation holes in eaves – these exist to prevent damp air building up in the loft and causing condensation. It might be worth checking that the roof has adequate ventilation (including roof vents in the sloping part of the roof) and getting these installed if needed.
Don’t fall though the ceiling! Only the wooden joists will bear your weight and it’s easy to have a moment’s inattention as to where you’re putting your feet while you’re working. With a second layer of insulation going across the top of the joists (and hence hiding them) it’s even easier to put your foot in the wrong place!
Don't forget to insulate the loft hatch – you need both an airtight seal around the edge and insulation across the back. To achieve modern standards of insulation, it is often easier to replace a traditional hatch cover made out of a painted plywood square with a pre-insulated hatch – this gives an opportunity to increase the size and include a folding ladder to make the loft a far easier place to access.
Flat roofs
Flat roofs can be insulated in several different ways:
Adding a layer of insulation on the top, followed by a new waterproof layer; this is called a "warm roof" as it keeps the structure of the roof on the warm side of the insulation. The roof surface could end up 20-30cm higher than it was prior to insulation.
Adding a layer of insulation into the gaps between the roof joists; this keeps the roof at the same level but either the surface of the roof or the ceiling underneath has to be broached to get the insulation in.
Adding a layer of insulation under the ceiling; this reduced ceiling height in the room below and is called a "cold roof" as the structure if the roof is on the cold side if the insulation - care must be taken to avoid condensation
Another twist on a warm roof is to build a green roof (I.e. a roof covered in plants) on the surface of the roof. This provides a surprising mount of both insulation and cooling (as well as promoting biodiversity and looking fantastic!) It's important to ensure the roof structure can take the additional load of the plants, growing medium and the water held by the green roof system.
Floors
Exposed floorboards look fantastic, but taking up carpets can increase heat loss through the floor! Losses through a traditional timber floor can be mitigated by either placing insulation under the floor or by filling gaps between the boards. Insulating under the floor is far easier if there’s a way of getting to the underside of the floor (e.g. through a cellar or crawlspace) as this avoids taking floorboards up.
Modern concrete floors should sit on an insulating layer, but many older ones might have no insulation underneath – in this case the only option is to put an insulating layer over the top.
In a multi-story home, it is worth considering insulating between levels (e.g. by putting insulating slabs into the gaps between floor joists.) This stops heat rising into areas in which it is not needed (e.g. a guest bedroom) and works particularly well when combined with a zoned heating system.
It's important to ensure adequate ventilation under floors to prevent damp, and hence the risk of rot. This is usually achieved by placing air bricks at a low level around a property to encourage airflow under the floor. However, this can make floors rather draughty; a new innovation to improve this is the automatic air brick. This has a moisture sensor connected to a shutter that can close the vent, so it only admits enough air to prevent dampness.
Pipes
Pipes should be insulated to keep the heat in. This is most common for pipes feeding hot water taps, of between a boiler and a hot water tank, buy can also be applied to central heating pipes passing through areas where heat is not required (i.e. where the heat leaking from the pipes isn't actually helping to heat the area!) Insulating these hot pipes can also enhance safety by avoiding people (particularly children and vulnerable adults) burning themselves by touching the pipes.
Cold water pipes should also be insulated to stop them getting so cold that they freeze and potentially burst in cold weather. This is particular important where they run through unheated areas (e.g. insulated lofts) and on the exterior of houses (e.g. to a garden tap – special insulated jackets are available for garden taps!) In some cases (e.g. where a cold water pipe runs close to hot water pipes, insulating the cold water pipe can prevent the water coming out lukewarm, and hence the temptation for someone after a cold drink to wastefully run the water until it's cooler!
The most common (and easiest to fit!) type of pipe insulation is a foam jacket shaped to fit common pipe sizes; this comes in approx 1 metre lengths which simply clip over the pipes; it helps to use ty-raps to secure these in place – these should be tightened enough to close the gap where it clips over the pipe but not so much that it squashes the insulation and hence reduces its effectiveness.
Tanks
There are several types of water tanks in most houses:
A hot water tank (often in an airing cupboard) where water fed to hot taps is heated. People with combination ("combi") boilers don't have these as their water is directly heated by the boiler.
A cold water tank (usually in the loft) where the pressure of the incoming cold water supply is dropped to suit a low-pressure hot water system. These are slightly old-fashioned now as high-pressure hot water systems become more common.
A header tank (usually in the loft) to regulate the pressure in a central heating system - again, these are becoming less common as modern heating systems are run at a higher pressure
It's clearly worth insulating the hot water tank – although most modern tanks come with moulded-on insulation, older tanks might be less well insulated. It's easy to clip a jacket around them to further reduce heat loss. The tradition of putting these tanks into an airing cupboard to create a pleasantly warm environment is an example of putting sources of residual waste heat to beneficial use!
Cold water tanks and header tanks should also be insulated with a suitably-sized jacket. this is particularly important if you upgrade the loft insulation, making the loftspace colder! In some cases (e.g. you have a combi boiler) it may be worth considering if you still need a cold water tank at all.
Gaps and draughts
While not technically insulation, there's a lot of energy that can be saved by hunting down and fixing gaps that allow unwanted draughts to carry off heated air or to let cold air in.
Door brushes are a relatively easy way of stopping draughts under both external and internal doors – and a lot more effective than the stuffed fabric sausages that used to be placed against the bottom of draughty doors!
Draught excluder strips fix draughts around door frames. They are available in different thicknesses to suit the size of the gap. Not all draught excluders are created equal – we find that the strips with a "P" cross-section are far more effective and last longer than the more common rectangular foam section strips.
Flexible mastic (e.g. around the base of skirting boards) is an easy and effective way of reducing draughts!
What’s coming up this month?
Discussion: Those interested are invited to an informal discussion of this month’s topic during post-service refreshments on Sunday 1st September at 11.15am - 12.15pmin the corner of the hall. Please come along and share your questions and your experience of and issues encountered investigating insulation; you can share as much or as little as you wish about what you have learned!
2nd August was Global Earth Overshoot Day – the day when we have used up the global resources that, if we were living sustainably, would have lasted all year. Look at https://overshoot.footprintnetwork.org/ to learn more about this.
There will be a bike maintenance morning at St. Andrew’s on Saturday 21st August between 10am and 12.30pm – this is open to all, so spread the word! Come along to get your bike checked and to learn more about cycle maintenance – it’s an opportunity to get restarted with that bike that you haven’t used in years (or to get that eBay/Freecycle find ready to ride!) It is possible just to arrive but it will help our planning if you can email iangsmith@ntlworld.com in advance with some idea of what time you may wish to arrive and what, roughly, may need to be done to your bike.
Once you’ve got your bike ready, why not join the Beds and Herts Historic Churches Trust “Bike and Hike” around local churches which takes place on Saturday 14 September 2024; see details in the church newsletter. While you can do this by yourself, we’ll be organising a group following a low-traffic route for less confident cyclists so you can build your confidence!
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