A Beginners guide to insulation part 2

In this blog I will be explaining various ways of insulating a new build property. This follows on from the first blog where we went over retro fitting insulation to an older property.

Hopefully this should be simple enough to understand and give you an idea of what you might require before you embark on your self build project.

It should be said right at the start it is always a must to get a qualified architect on board. Being able to calculate the types and thicknesses of insulation to meet building regulations are a must.

So lets start from the ground up…

Some properties depending on ground conditions can require what is called a clay heave board. Although this board is not technically insulating, it is a polystyrene insulation board. This is required where ground conditions are shrinkable type clay. This clay soil dries to a crazed texture and when wet expands. Changes in the soil like these are called clay heave. Causing severe problems to the foundations when this shift occurs can be solved using a clay heave board. Claymaster and Claylite are a few of the brand names of these boards. Being a low density expanded it absorbs the pressure placed on the foundations as the ground moves.


Various types of floor insulation are available which we will cover in part 3 of this blog. As heat rises and pushes warm air up the heat will generally escape through the roof. Interestingly the ground below your home will usually be warmer than above so why does it make sense to insulate the floor?. Well insulating the floor combined with the rest of the insulated structure provides an envelope of insulation. This ensures the best possible result slowing down the loss of heat and retaining it.


This example of floor construction can be cold as the air circulating underneath is causes draughts. Different types of insulation are used in this example of construction, These could include a rigid PIR foam type insulation , fibreglass semi rigid batts or fibreglass roll. These types of insulation would be placed in between the timbers to fill and leave no gaps.



General Purpose Ecotherm Insulation


This is where the construction has either a concrete slab , concrete plank or a block and beam system. With this example of floor the insulation would usually be PIR or phenolic foam insulation. The make up of this would be concrete slab the DPM then insulation. Followed by another layer of DPM which would be covered by the floor screed. Important to note is that some screeds react to the foil on the insulation hence the layer of DPM above.



celotex insulation cg5000Cavity wall insulation is usually the starting point of where an architect would start their calculations. Given that the majority of heat is lost through the walls (see part 1) this is of great importance. There are many different types of cavity wall insulation to choose from. Including a partial fill PIR insulation board or Phenolic insulation. Alternatively you might go down the full fill insulant route such as P

IR , Phenolic , Rockwool or Fibreglass insulation. The reason you would go for full fill would be to reduce the insulation required on the inside skin of the property.

I personally am not a fan of full fill and like to see a 50% void in the cavity. As cavities were always designed to allow moisture and air flow it makes sense. In a partial fill the insulation would be installed using wall ties and clips to hold it against the inner skin. In Full Fill it does what it says and fills the cavity apart from rigid board which generally fills 90%.

When using a timber frame construction it is usually advise to use a fibreglass breathable type insulation. Fibreglass timber frame batts and roll are available for this purpose also in some instances a multifoil insulation can be used.


Firstly I will cover the inner skin of the external walls. These walls if required to be insulated generally would be insulated using a pre insulated plasterboard which would provide a two in one function. This insulation could be fixed using drywall adhesive and mechanical fixings or just fixings alone. In some places where noise is a problem an acoustic fibreglass or mineral wool insulation can be installed. Now the internal walls if constructed using track and stud are also insulated. This helps zone the property if you require one room to be warmer or cooler than another.

Acoustic partition roll or Acoustic batts are generally used in these wall constructions. However fibreglass loft roll can be used but will not reduce the passage of sound as much. Another way of insulating the walls which is more thermally efficient would be to use PIR insulation or Phenolic insulation. Multi-foil insulation has seen an increase when insulating the internal walls over the past few years.


Although not really thought about when insulation is mentioned it is a very important subject. Nowadays double and triple glazed windows and doors are generally quite thermally efficient. It is important however to check with the manufacturer what level their windows and doors achieve. This is because there are cheaper ‘B’ rated versions of double glazing made that are not as thermally and acoustically efficient as ‘A’ rated.


ecotherm roof insulation boards

Recticel roof insulation boards for use in pitched roof and flat roof insulation projects

Roof insulation is a huge area to explore when insulating a property. This often comes down these days to whether or not the roof space is being used. There are different types of roof construction so lets start with the pitch. Pitched roofs can be built in what’s called either a warm roof or cold roof construction. Warm roof insulation is where the insulant is placed over the top of the rafters or joists and fixed with warm roof fixings.

Cold Roof construction is where the insulation is placed between the joists or rafters. The obvious advantage is that with a warm roof project you do not lose any headroom in the loft. With a cold roof you may have to insulate below the rafters as well as in between to reach the target ‘U’ value. Hence losing precious headspace in the loft. Both multifoil and PIR / phenolic insulation can be used in both instances. If multifoil is being used there are specific types such as Superfoil SF19BB with a built in breather membrane. When building a cold roof construction you always have to cover the underneath of the rafters with insulation. Essentially this eliminates any possible cold bridging through the timbers. The downside to this is you then start to encroach into the headspace of the loft.




Quite often in a new build property the loft is being used as a room. But if this is not the case then insulating the floor is a great option. This can be done using PIR insulation in between the joists. Alternatively if you are not using the loft for storage either then use fibreglass loft roll. Fibreglass loft insulation is the cheapest method to efficiently insulate your loft floor. At the time of writing current regulations only require 270mm thick. This is achieved with one thickness filling the depth of the joists with another layer cross layered.



Hopefully this has been a little help if you are a novice when it comes to insulation. Todays construction designs are all about air tightness and insulation. Together these ensure that there is a large reduction in the passage of warm air from the property. We are moving ever closer to the requirements to use less and less fossil fuels to heat our homes. Quite rightly we should design new properties to reduce the need for excessive energy. Insulating your home properly and making an airtight environment along with proper ventilation can achieve this. There are lots of ways to do this including heat recovery systems that recycle the heat from your home with fresh air. Ground source heat systems which use the heat from underground to warm your home. These along with many other systems mean that we can achieve a greener future and hopefully save money.

For various insulation materials available on the market please see part three of this blog coming very soon. Alternatively contact BMD Insulation