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The 4 most commonly used types of building membrane

Help! My builder says I need a membrane.

Which one do I need and why?

There are a number of different membranes which can be used within the building structure, each performs a different role and has different properties to offer. It is important to understand what each one does before you go ahead and purchase. Below, we give you a brief overview of the 4 most commonly used types of building membrane, then go on to answer one of the most common questions we get asked: “What is the difference between a VSD membrane and a Breather Membrane?”

The 4 most commonly used types of building membrane are:

High vapour resistance Roofing Felt
Vapour control layer
Variable Surface Diffusion ‘Intelligent’ membrane
Breather Membrane

High vapour resistance Roofing Felt:

Why do we use High vapour resistance Roofing Felt?

Traditional roofing felt is a material typically made of a base fibre which is then coated with asphalt or tar. It is waterproof and is highly resistant to moisture/water vapour.

Although breather membranes have become increasingly popular due to their improved performance and durability, roofing felt is still commonly specified in building work if bats are present in the structure or by a conservation officer in a listed property / historic building to preserve the originality of the structure.

Vapour Control Membrane

What is a Vapour Control Membrane?

An air and vapour control membrane is an airtight membrane made of plastic or foil which is used to reduce the movement of warm moist air from the inside of the building and stop it penetrating through to the actual building fabric. It is installed on the warm side of the insulation i.e., the inside of a pitched roof or the interior walls.

How do Vapour Control Membranes actually work?

Vapour control membranes have one job and that is to stop moisture travelling from the inside of the building (i.e., the internal rooms) and through to the building fabric itself. This in turn designed to protect the building fabric from mould growth, decay and low air quality. Vapour control membranes do not allow moisture to travel back in to the building fabric which can be problematic as moisture gets trapped behind the membrane and has no means of escape.

Variable Surface Diffusion (VSD) Membrane

What is a Variable Surface Diffusion (VSD) Membrane?

Thermofloc Variable Surface Diffusion (VSD) is classed as an intelligent membrane, acting as an air tightness and vapour control membrane whilst allowing two-way movement of water vapour as conditions within the building allow.

Where do you install a VSD Membrane?

The VSD membrane is installed on the inside (warm side) of roof construction and the inside (warm side) of walls of timber frame structures and studwork,

What does a VSD membrane do?

VSD Membranes are used in building construction to control the movement of water vapour from the inside of the building and through to the building fabric itself, helping to prevent condensation from forming on the inside of the building fabric which can lead to mould growth , decay and low air quality. Because VSD membranes can effectively resist air pressure, they are used to improve air tightness and minimise air leaking within the building fabric.

How does a VSD membrane work and what is the difference between a vapour control membrane and an intelligent membrane?

As with a vapour control membrane, when humidity levels are high within the building, a VSD membrane will be vapour closed, i.e. they have a high vapour resistance. This prevents the water vapour in the humid air travelling through to the building fabric and forming interstitial condensation which in turn creates mould and decay.

The difference between a vapour control membrane and an intelligent membrane is that once the humidity levels drop then the ‘intelligent’ membrane will open up (vapour open state) and allow any trapped water vapour to escape. So, moisture that does enter the building fabric is able to back diffuse out of the building as the humidity levels decrease.

So now we have looked at the difference between the membranes installed on the warm side let’s take a journey to the cold side. ( the outer side nearest the wall/roof.)

Breather Membranes

What is a Breather Membrane and why do I need one?

Breather Membranes are semi-permeable membranes designed to allow excess water vapour to pass from the inside of the building fabric out into the atmosphere, whilst preventing moisture, surface water or rainwater from entering from the outside.

They are installed on the cold side (outer) of the insulation – so the outside of a pitched roof, on the underside of suspended floor joists, or the exterior walls of a timber frame building, or sometimes against the inside surface of a solid wall after the insulation.

The use of a Breather Membrane will help to prevent condensation, mould and decay within the fabric of the building which in turn helps to maintain humidity levels and create a healthier living/working environment.

How do Breather Membranes work?

Installed on the cold side of the insulation -The inside face of the Breather Membrane contains pores or holes which allow water vapour and other gas molecules to pass through from inside to the outside of the building.

Because these gas molecules are incredibly small (less than 3 millionths of 1mm) the membrane can appear solid to the naked eye but will still allow large quantities of water vapour to pass through.

The outside of the membrane stops liquid water ingress (rain/snow) from the outside of the building to the inside, serving as an extra layer of protection within the roof or wall when the cladding material itself may not be watertight (e.g. tiles)

Where do I use a Breather membrane?

Breather membranes are primarily used in roofs and walls but can be used on the underside of suspended floor joists from below.

They help keep the roof space dry, prevent condensation and maintain the effectiveness of the insulation.

In walls, breather membranes are installed behind the exterior cladding. They contribute to moisture management, a more energy-efficient building and will assist in maintaining a consistent indoor temperature by reducing heat loss through the walls and preventing drafts.

What if I don’t use a Breather Membrane in my roof or wall?

If you decide not to use a breather membrane you risk water passing through the tiles / stone/cladding on the external side. A build-up of water in a structure is never good news. Excess moisture rots timbers, creates damp, allows mould spores to thrive and renders any insulation ineffective, all of which leads to an unhealthy building and in turn an unhealthy living environment.

Thermafleece Breather Membrane – which way is up?

Thermafleece Breather Membrane has two sides. A grey side which has a higher UV stability than the other white side. When installing, the grey side should face outward (the cold side) and the white side should face inward toward the inside of the building (the warm side). For example, when installing in a floor, the grey side faces the ground and in a roof, the grey side faces the sky.

Joints in the membrane can be sealed with a breathable tape to prevent accidental air leakage, although this is not essential.

Do I need to use a Breather Membrane when insulating a suspended floor?

A Breather Membrane can be used to support insulation (hammocking) between suspended floor joists

The membrane can be nailed or stapled to the underside of the floor joist if access permits.

Coverage and overlapping a breather membrane

When installing onto a wall or pitched roof, 1 roll of a membrane with 75m2 coverage will actually cover about 60m2 allowing for overlaps.

If you are hammocking the membrane for a suspended floor then one 75m2 roll will cover approx. 45m2
There is no need for a membrane if you are insulating your loft, although because lofts are inherently dirty, and debris tends to fall down from the roof, many people use them as a cover over the insulation to help keep it clean.

For further advice and installation diagrams take a look at our help and advice section https://naturalinsulations.co.uk/help-advice/

For product information and factsheets go our product section https://naturalinsulations.co.uk/membranes/

For further information on Eden Renewable Innovations Ltd – The manufacturers of Thermafleece go to the website www.thermafleece.com

Loft insulation – keeping you toasty and saving you money

Insulation saves heat and heat costs money. So, it’s a simple fact that if you’re saving heat, you’re saving money. The more you insulate the more heat you save and the less money you spend. There is no better time than the present to check your existing insulation and make sure your loft is properly insulated for the autumn and winter ahead.

The more you insulate the more you save

If the existing insulation is in good condition and measures 270mm or more in depth, then you shouldn’t need to install more insulation. However, if your loft is full of old insulation which has slumped and degraded, then the last thing you want to do is install more of the same. If you do, someday you’ll return, look at the same scene and repeat the same exercise. Instead, use something that won’t slump or degrade and buy something that lasts. A natural fibre insulation which is thermally bonded with recycled polyester such as Thermafleece British Sheep’s Wool Insulation will ensure the insulation retains its loft and once you insulate, you won’t have to do it again.

There are also many other benefits of installing a natural fibre insulation: As well as keeping in heat, natural fibre insulations will help manage summer heat gain; help with moisture and humidity levels; reduce noise and improve sound quality. They are none itch, safe to install and can improve indoor air quality, sustainability, health and well-being inside your home.

The More Insulation the Better

The more insulation you can install the better, but typically you should install a natural fibre insulation to a depth of 240mm. It is not always necessary to remove your existing insulation. As long as it is in fairly good condition and there is no signs of water damage then you can top up with a good quality natural fibre or recycled polyester insulation.

In most lofts, it’s easy to install a deep layer of insulation. If you decide to board part of your loft you can use loft legs to raise the level of the boarding. This will still allow you to install a deep layer of insulation.

Remember that around 5% of heat is lost through your loft hatch, so it should also be insulated.

In a new property with a well-ventilated loft, a recycled polyester insulation such as SupaSoft Insulation will be very effective. SupaSoft insulation is a great way to use recycled single use plastics. It’s also safe to handle and itch free.

For an older property or if loft ventilation is limited, use a natural fibre insulation such as Thermafleece CosyWool Roll. As well as being safe, sustainable and healthy, natural fibres can help regulate humidity levels. They do this by absorbing moisture and holding it in a safe form. It’s then released it as air around it becomes less humid.

In a nutshell

In a nutshell: Insulation does much more than prevent heat loss so give this some thought when you decide what’s right for you. Choose a good quality insulation which will last the lifetime of your building. You’ll never have to do it again and remember that over its life, insulating is never a costly investment.

How much insulation do I need in my loft?

How do I measure and calculate how much insulation I need in my loft?

It is important to take the time to work out how much insulation you need to ensure you get the best fit and also, so you don’t over or under order. Planning the installation is an important part of the job and correctly laid insulation significantly improves thermal performance.

When insulating using Thermafleece we recommend you should install to a minimum depth of 240/250mm and ideally 300mm particularly for new build properties. You will need to install one layer between the ceiling joists and one or more layers above the level of the joists. The insulation above the joists is cross-laid over the joist meaning it runs perpendicular to the direction of the joist. The joists are the horizontal timbers that support the ceiling below the loft. These are often confused with rafters which are the angled timbers that support the roof.

There are 3 simple steps to measuring for your loft

Step 1. Measure the total loft space.

This will provide a total square metre requirement. Simply multiply the length (in metres) by the width (in metres) of the loft to calculate the area in sq.m. For the layer of insulation that is fitted between joists, deduct 10% of the loft area to account for displacement of the joists. For insulation layers that sit above the level of the joists take the full loft area. If you can’t access the loft or to give yourself a sense check, simply measure the outside of the building for dimensions.

Step 2. Measure the space between your joists.

Measure the width between joist ensuring the tape measure runs perpendicular to the joist. Repeat this to determine the minimum and maximum spacing between joists. This will allow you to determine the width of insulation required to fit between joists. Often and especially in older properties the width does vary but several width options are available, and Thermafleece is a quilt material which is forgiving against the timbers. Thermafleece is available in a variety of widths. This is only required for the layer of insulation fitted between joists, layers cross-laid over joists do not need to fit between anything so we generally recommended our widest widths for this.

Step 3. Measure the depth of the joists.

Typically, if your joists are 100 mm thick, we would recommend you full fill the joists with 100 mm thick. To increase the thickness and eliminate heat loss, we would recommend 100 between and at least 140 mm over the joist. This generally means that you put one layer between the joists then other layers running above the joists across the direction of the joist.

Example Using Thermafleece CosyWool Roll.
Space between joists is 350mm. 370mm insulation width required.

Loft Area – 9 metres x 7 metres = total area 63m2

Joist depth – 100mm

Recommended Insulation depth is 240mm

Between the joists:
100mm thick x 370mm wide. 3 rolls in a pack and total m2 of one pack is 7.22m2

Area required is 63 sq.m less 10% = 56.7 sq.m

56.7 square metres ÷ 7.22 square metres per pack = **7.85 packs

You would need to order 8 packs of 100 x 370 which will provide you with 57.8 sq.m to go between the joists.

Cross-laid over the joists *
140mm deep x 570 wide 2 rolls in a pack and total m2 of one pack is 5.24m2

63 square metres ÷ 5.24 square metres per pack = ** 12.02 packs

You would need to order 12 packs of the 140 mm x 570mm which will provide you with 62.88 square metres to go crossways over the joists.

*Remember: Layers cross-laid over joists don’t need to fit between anything so we generally recommended our widest widths for this

**We don’t split packs so depending on how generous your measurements are, round up or down

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Find out more:

Further information is available in our Help and Advice Section: https://naturalinsulations.co.uk/help-advice/

Thermafleece British Sheeps Wool: https://www.thermafleece.com/

Featured Image is from the Cold Roof Application Notes, one of a series available in the Help and Advice Section

Insulation, the solution to our mountain of wool?

On the face of it, the current surplus of wool should provide a greater opportunity to make insulation from British sheep’s wool. However, putting this into practice is more complicated than it first looks. We look at the issue and tackle some of the challenges we face.

Global demand for British wool has fallen sharply this year but supply of British wool has remained constant. The price of most wools has plummeted, and the market has ground to a near halt. Naturally, farmers are looking at new end-uses for their wool. As well as seeking to stimulate traditional end-uses such as carpets, fabrics, and knitwear.

All wool isn’t the same

Natural crops vary widely in their type, form, and application. Wool is no exception. Wool types range from very fine to very coarse, short to long and light to dark. These properties affect the grade, price of the wool and end-use. It’s the same as timber varying from softwoods such as pine to fine hardwoods such as walnut. Each has their own properties and uses, some functional and some aesthetic.

Established more than 20 years ago, Thermafleece is a very effective use for coarse dark wool that is unsuitable for familiar applications. Coarse dark wool is suited for wool insulation because it doesn’t need to feel very soft against the skin and it doesn’t need to be dyed. For wool insulation, the dark colour and coarseness aren’t a problem. It’s also the lowest cost of all wools making the final insulation competitive.

Will wool insulation save the day?

Farmers are now considering insulation as an alternative way to get a higher price for their surplus wool. Thanks to the success of Thermafleece and the government’s recent focus on energy efficiency. But is this viable?

A lot of the surplus of wool is higher grade than typical coarse dark insulation wool. The higher grade wool is usually destined for higher value items such as carpets, fabrics, and knitwear. Using higher-grade wool in insulation is like using walnut or rosewood to build your garden fence according to many. Others believe the wool is sitting doing nothing so what better use than insulation.

The higher grade wools can be used in wool insulation but because they cost more, the insulation will be significantly more expensive compared to coarse dark wool insulation. What’s more, there are no added benefits using higher grade wool when it comes to insulation. There’s a conundrum. How can you make competitive insulation from higher grade wools and give the farmer a fair price for the wool? In short, you can’t without subsidising the cost of the insulation or the cost of the wool.

Luckily, the Green Homes Grant Scheme will substantially subsidise the cost of having sheep’s wool insulation installed in your home. But why would you use wool insulation made from higher grade wool when coarse dark wool insulation does the same job at a lower cost? Our conundrum resurfaces. How do we make competitive insulation from higher grade wool and give the farmer a fair price for the wool?

What now?

We should promote the benefits of British wool as a fantastic high-quality raw material worthy of many high value end-uses. Insulation is a great end-use for coarse dark wool and other low grades of which there is plenty. But we should focus on higher value end-uses for higher quality wool rather than insulation. British wool is one of the best materials in the world. It produces high quality durable, functional and beautiful products compared to man-made fibres or wools of other origins. And that’s where the wool industry’s efforts need to be.

By Mark Lynn Thermafleece MD and Vice Chair of the ASBP .

Want to find out more about British Wool:
Visit our Help and Advice Page for application notes and further information: https://naturalinsulations.co.uk/help-advice/

British Wool Website: https://www.britishwool.org.uk/
Campaign for Wool: http://www.campaignforwool.org/

Convert Your Garden Shed or Shoffice

According to national statistics, more than 1.5 million people are now working at home. With space limited, what better way to create a comfortable working space than to convert your garden shed or shoffice? And what better way to make the space comfortable than to insulate with Thermafleece British sheep’s wool insulation?

Thermafleece is truly breathable meaning it will help regulate moisture within the fabric of the shed and help create a more stable structure. It’s also made in the UK from British wool so it’s an ideal sustainable choice.

Before you start

Before you start to convert your garden shed or shoffice, it’s important to be aware that most sheds weren’t designed with insulation in mind, so you need to take a few considerations into account.

You will have to minimise the risk of water getting into the insulation from outside and you must minimise the risk of condensation forming from the inside. This is done by using breathable membranes against the inside of the shed wall and using vapour control membranes against the warm side of the insulation. The warm side of the insulation is the bit you see when you are inside the shed. We explain in a bit more detail below.

Insulating the walls

Unless the roof overhangs the wall quite significantly, you will need to insulate the walls from the inside. If you add insulation on the outside of the walls and the roof doesn’t overhang, then the wall insulation will stand out from the roof line and most likely trap water.

How much insulation you install depends on the depth of the timber frame and the amount of space you can afford to lose. The simplest thing to do is to install insulation between the timber frame which is usually around 50mm in depth. If you extend beyond the frame depth you may need to make adjustments around the window reveals. Thermafleece CosyWool Roll comes in a variety of thickness to suit most frame depths.

Before you install Thermafleece between the wall frame, you should take measures to ensure rain can’t penetrate the insulation. If the shed is already clad with timber, install a breathable membrane fitted against the inside of the wall running over the frame. Ensure that top layers overlap bottom layers of the membrane to allow any penetrating water to run freely down. You can also tape joints in the membrane.

Install Thermafleece between the timber frame once the breather membrane is fixed. You can staple the insulation to the timbers in order to secure it although the friction between the timber and insulation will be enough to hold it in place.

Once you have installed the insulation, fit a vapour control membrane on the inside secured to the frame ensuring all joints are taped. You can then fix your internal lining.

Insulating the roof

As with the walls, the simplest way is to insulate the full depth of the timbers making up the roof. The roof should be weather-tight, so you don’t need to install a breather membrane to the underside of the roof. If there are any leaks in the roof, make sure these are repaired prior to insulating.

Install Thermafleece between the timber frame in the roof. You should install a vapour control membrane underneath the insulation fixed to the roof timbers with all joints taped. It is particularly important to install a vapour control membrane to the underside of the roof because there is no ventilation under the roof and the roof has a high vapour resistance, so you want to eliminate the risk of moisture getting to the underside of the roof.

Insulating the floor

If you are going to insulate the floor, you can fix battens on top of the shed floor and insulate between. Install a vapour control membrane over the battens and tape all joints before fixing flooring on top. Be mindful of ways water can penetrate the floor so make sure the vapour control membrane on the walls is securely taped to the vapour control membrane on the floor.

And finally

Put the kettle on, put up your feet, enjoy the space and don’t forget to get some work done.

By Mark Lynn Thermafleece MD and Vice Chair of the ASBP .

Take a look at our FAQ’s for more information
Our Help and Advice Page has a number of Presentations and Briefing papers for you to read
For more information on Thermafleece Sheep’s Wool insulation visit www.thermafleece.com