INSULATED PLASTERBOARD INSTALLATION: TO USE OR NOT TO USE A VAPOUR BARRIER?*

London and other similar areas often rely on insulated plasterboard to enhance the energy efficiency of walls and ceilings, especially in moist conditions where dampness and condensation can be a concern. Insulated plasterboard consists of a layer of insulation material, such as expanded polystyrene, PIR (PolyIsocyanuRate) or Phenolic Foam bonded to the back of a plasterboard panel. However, when installing insulated plasterboard, the question of whether or not a vapour barrier is necessary can arise. In this blog, we'll explore the reasons why a vapour barrier may or may not be necessary, and what factors should be considered.

 

 Table of contents

  • INSULATED PLASTERBOARD INSTALLATION: TO USE OR NOT TO USE A VAPOUR BARRIER?
  • INSULATED PLASTERBOARD- TO USE OR NOT TO USE A VAPOUR BARRIER?
  • WHICH INSULATED PLASTERBOARDS HAVE BUILT-IN VAPOUR CONTROL LAYER?
  • CAN DAMP COME THROUGH INSULATED PLASTERBOARD?
  • DO I NEED A VAPOUR BARRIER WITH KINGSPAN/CELOTEX/XTRATHERM?
  • DOES CELOTEX INSULATED PLASTERBOARD HAVE A VAPOUR BARRIER?
  • TYPES OF FOIL-BACKED PLASTERBOARD 
  • INSTALLING INSULATION WITHOUT A VAPOUR BARRIER: PROS AND CONS
  • INSULATED PLASTERBOARD BUILDING REGULATIONS
  • INSULATED PLASTERBOARD PRICE
  • CONCLUSION

INSULATED PLASTERBOARD- TO USE OR NOT TO USE A VAPOUR BARRIER?

To answer the question of whether a vapour barrier is needed when installing insulated plasterboard, it is necessary to understand the construction of this compact product.

Insulated plasterboard is a fairly complex product consisting of a gypsum board attached to a layer of insulation, which in turn, depending on the type of insulation, may or may not have a built-in aluminium vapour barrier.
Today, it can be confidently said that the increasing competition in the UK market has forced almost all manufacturers, such as Celotex, Kingspan, and Xtratherm, to use such foil on the insulation core. In addition to being a built-in vapour control barrier, it also provides excellent reinforcement to the insulation core. Additionally, it serves as a barrier against rodents and, most importantly, reflects heat or cold in the opposite direction.
Generally speaking, it is not necessary to use a vapour control layer when installing insulated plasterboard using the Dot and Dab method. The technology itself excludes its use. However, it is different in the case of mechanically mounted insulated plasterboard on the wall or ceiling.
When installing insulated plasterboard using the mechanical method, such as with screws, it is recommended but not necessary to use a vapour control layer. The best example of this is insulation in the loft. Here, a VCL is used for two reasons. The first is to seal the attic from wind, and the second is, of course, as a moisture barrier.
Similarly, when installing insulated plasterboard to a ceiling separating the upper floor of a house from a cold attic, a yellow or green VCL barrier is used and an additional layer of insulated plasterboard is added for extra insulation.

 

WHICH INSULATED PLASTERBOARDS HAVE BUILT-IN VAPOUR CONTROL LAYER?

Generally speaking, there are not many manufacturers of such boards in the UK. The most well-known ones include Xtratherm XT/TL, Kingspan K118, and Celotex PL4000. Here is a list of the most frequently purchased thicknesses of insulated plasterboard with built-in vapour control layer:

 

PHENOLIC CORE

Xtratherm SR/TB Safe - R Thermal Liner - 37.5mm, 52.5mm, 62.5mm, 72.5mm, 87.5mm, 92.5mm, 112.5mm.

Kingspan Kooltherm K118 - 32.5mm, 37.5mm, 42.5mm, 52.5mm, 57.5mm, 62.5mm, 72.5mm, 82.5mm, 92.5mm.

 

PIR CORE

Xtratherm XT/TL Thermal Liner - 24.5mm, 27.5mm, 29.5mm, 32.5mm, 34.5mm, 37.5mm, 39.5mm, 42.5mm, 44.5mm, 47.5mm, 49.5mm, 52.5mm, 54.5mm, 57.5mm, 59.5mm, 62.5mm, 64.5mm, 67.5mm, 69.5mm, 72.5mm, 74.5mm, 77.5mm, 79.5mm, 82.5mm, 84.5mm, 87.5mm, 92.5mm, 99.5mm, 102.5mm, 109.5mm, 112.5mm, 119.5mm, 122.5mm.

Celotex PL4000 PIR Thermal Insulated Plasterboard - 27.5mm, 32.5mm, 37.5mm, 42.5mm, 47.5mm, 52.5mm, 57.5mm, 62.5mm, 67.5mm, 72.5mm, 77.5mm.

Ecotherm Eco-Liner - 37.5mm, 42.5mm, 52.5mm, 62.5mm, 72.5mm, 82.5mm.

Speedline PIR Thermal Laminate Board - 37.5mm, 62.5mm, 72.5mm.

Warmline PIR Insulated Plasterboard - 27mm, 29mm, 35mm, 38mm, 48mm, 50mm, 60mm, 62.5mm, 70mm, 72.5mm, 80mm, 82.5mm, 90mm, 92.5mm, 102mm.


CAN DAMP COME THROUGH INSULATED PLASTERBOARD?

Dampness can, however, it should not in any way pass through the warm side of insulated plasterboard. There are several basic examples of when dampness can pass through insulated plasterboard: 

  • when the VCL layer has been damaged,
  • when it is not continuous - in other words, it has gaps, 
  • when there is a significant moisture buildup associated with lack of ventilation. 

To prevent this, it is necessary to:

  • attach an additional layer of aluminium tape to the board joints to ensure the continuity of the vapour barrier layer,
  • provide adequate air exchange and remove excessive moisture from the building, 
  • avoid mechanical damage to the aluminium layer.


DO I NEED A VAPOUR BARRIER WITH KINGSPAN / CELOTEX / XTRATHERM?

If you are going to use branded, good quality insulated plasterboards such as Xtratherm XT/TL, Kingspan K118, and Celotex PL4000, you normally should not use a vapour control layer, if they are installed correctly. To find out how to install insulated plasterboards correctly, click here.

 

DOES CELOTEX INSULATED PLASTERBOARD HAVE A VAPOUR BARRIER?

Celotex insulated plasterboard such as PL4000 range products typically include a built-in vapour control layer (VCL) that acts as a barrier against moisture. Therefore, it is not necessary to use an additional vapour control layer  with such products.

 

TYPES OF FOIL-BACKED PLASTERBOARD

When it comes to application you can choose from standard insulated plasterboard commonly used on walls and ceilings and moisture resistant insulated plasterboard for wet rooms, bathrooms and shower rooms. 

MOISTURE RESISTANT PLASTERBOARD

Moisture resistant insulated plasterboard is backed with rigid polyisocyanurate foam insulation and two vapour barriers which are specially designed to use in wall lining and internal wall partitions. These boards are mostly used where both high thermal performance and high moisture resistance is required.

When it comes to thermal plasterboard performance you can choose from Phenolic, EPS (Expanded PolyStyrene), XPS (EXtruded PolyStyrene) and PIR (PolyIsocyanuRate) insulation core.

PHENOLIC FOAM PLASTERBOARD

Phenolic plasterboard is a premium performance insulation with a fibre-free rigid thermoset phenolic core. It provides a level of performance that is unrivalled in the world of rigid thermoset insulation materials with a thermal conductivity of just 0.018 W/mK across all thicknesses. It is a top-class three-in-one product for internal wall insulation used as mechanically fixed and adhesively bonded 'dot and dab' insulated plasterboard. For example, Kingspan K118 range is a high-efficiency phenolic insulation core with a certified thermal conductivity (lambda value) of 0.018W/mK factory bonded to 12.5mm premium plasterboard. Kooltherm K118 (previously Kingspan K18 and K17) provides high-levels of insulation, dry-lining and vapour control layer in one easily applicable 2400mm x 1200mm (8x4) insulating sheets.

PIR INSULATED PLASTERBOARD

Pir core wall panel is an insulated plasterboard combined of polyisocyanurate (PIR) rigid insulation foam core bonded to 9.5mm or 12.5mm tapered edge plasterboard that is suitable for internal applications, fixed with adhesive dot and dab direct bonding.


INSTALLING INSULATED PLASTERBOARD WITHOUT A VAPOUR BARRIER: PROS AND CONS

Installing insulated plasterboard without a vapour barrier can have both pros and cons. One of the biggest advantages of not using a vapour barrier is:

  • it allows the building to "breathe",
  • prevents the build-up of moisture within the walls- this can be particularly important in older buildings that were constructed using materials that do not allow for good ventilation, such as solid stone or brick.
  • it can make the installation process quicker and easier- vapour barriers can be fiddly to install, and if not installed correctly, they can actually trap moisture in the walls and cause more problems than they solve. By skipping the vapour barrier, installers can save time and avoid potential complications.

However, there are also some potential drawbacks to installing insulated plasterboard without a vapour barrier. One of the biggest concerns is:

  • the risk of condensation-without a vapour barrier, warm, moist air can penetrate the walls and condense when it hits a cold surface, such as the insulation or the outside of the building. This can cause water damage, mould growth, and even structural damage over time.
  • the impact on energy efficiency-without a vapour barrier, there is a greater risk of air leakage and heat loss, which can reduce the effectiveness of the insulation and increase heating bills.

It is important to weigh the pros and cons carefully before making a decision, and to ensure that the installation is carried out correctly to minimise the risk of problems in the future.

 

INSULATED PLASTERBOARD BUILDING REGULATIONS

Building Regulations are law and must be met when applied to any project over a certain size. Where 50 percent or more of the internal wall is being renovated building regulations would normally apply, and the thermal insulation of the wall would have to meet the standards required by building regulations approved documents. The regulation that refers to the thermal efficiency requirements when carrying out renovation or replacement work on an existing dwelling is explained in Approved Document L1B (ADL1B). For instance, to meet Part L when constructing an extension you need to meet a U-value of 0.28W/m2K. When new layers are added to a thermal element through being dry lined internally the U-value of 0.30W/m2K is required. If at least 50% of the element is being renovated then it should be upgraded to achieve the U-values as follow:

Pitched roof - insulation at ceiling level 0.16W/m2K.
Flat roof or roof with integral insulation 0.18W/m2K.
Pitched roof - insulation between rafters 0.18W/m2K.

Insulated plasterboard is not suitable for use on such walls where there is a risk of moisture penetration or on timber or steel frame construction. This method is only suitable for use on brick, blocks, concrete cavity or rendered solid walls which are dry, stable and most importantly free from moisture penetration. Where you don't have cavities in your wall you shouldn't adhesively bond because of the risk of moisture penetration from outside. In this particular situation you should always mechanically fix wooden battens and screw the plasterboard to battens.

 

INSULATED PLASTERBOARD PRICE

Because thermal plasterboard can be used in so many different situations, it is important to know you’re getting the best price, particularly if you’re working within a tight budget. If you are looking for the plaster-boarding cost per m2 you should be looking for £9.05 per m2 and £26.09 per sheet. This is based on British Gypsum Gyproc ThermaLine Basic insulated plasterboard. Here at InsulationGo we offer other top brands such as Kingspan, Xtratherm, and Celotex. We usually keep in stock our most favourite Kingspan K118 in 50mm thickness. 

In terms of performance all types of insulated plasterboards are classified in given order (based on 52.5mm thickness): 

1. Phenolic insulated plasterboard / Thermal Conductivity: 0.018 W/mK
2. PIR insulated plasterboard / Thermal Conductivity: 0.022 W/mk
3. XPS insulated plasterboard / Thermal Conductivity: 0.030 W/mk
4. EPS insulated plasterboard / Thermal Conductivity: 0.034 W/mk

In terms of prices, the insulated plasterboard list looks completely different (based on 32.5mm thickness). 

1. EPS insulated plasterboard / £38.03
2. XPS insulated plasterboard / £48.60
3. PIR insulated plasterboard / £57.08
4. Phenolic insulated plasterboard / £69.21

The cheapest product would be EPS bonded to plasterboard such as Warmline EPS Insulated Plasterboard, British Gypsum Gyproc Thermaline Basic or Knauf EPS Thermal Laminate. On the other hand, the most expensive insulated plasterboard would be phenolic insulated plasterboard such as Kingspan Kooltherm K118 or Xtratherm XT/TL Thermal Liner. Those boards are the most effective type of rigid phenolic insulation boards currently available in the UK.

 

CONCLUSION

In conclusion, the decision to install insulated plasterboard with or without a vapour barrier depends on various factors, including the building's construction, ventilation, and moisture levels. While a vapour barrier can provide additional protection against dampness, it may also trap moisture inside the walls if not installed correctly. On the other hand, installing insulated plasterboard without a vapour barrier can offer more flexibility and simpler installation, but it requires careful monitoring of the building's moisture levels and proper ventilation. Ultimately, it's essential to consult with building professionals and follow manufacturer guidelines to ensure the proper installation of insulation and vapour barriers.

 

Related articles:

DEBUNKING THE TOP 3 MYTHS ABOUT VAPOUR BARRIERS AND FOAM RIGID INSULATION

INSULATION BACKED PLASTERBOARD THICKNESS

THE DANGERS OF OVER INSULATING YOUR HOME

VAPOUR CONTROL LAYER. DARK SIDE

 

 

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