8th Mar 2024 -

Moisture is damaging to building insulation. When moisture reaches insulation materials, it compromises their ability to provide high performance and durability. Preventing moisture issues should be a top priority to build energy-efficient, long-lasting structures. 

Celotex insulation offers excellent solutions for maintaining dry building envelopes. This feature explores ways Celotex helps to control risks around bulk water, vapour diffusion, air leakage and condensation. 

What is the relationship between moisture and insulation?

Moisture causes harm to insulation materials. Even small amounts of water cause its performance and durability to suffer.

Loss of R-valueInsulation works by trapping air to resist heat flow. When moisture invades, it displaces trapped air and reduces the R-value. Even small amounts of water can markedly diminish thermal resistance.
Promotes mould and rotExcess moisture allows mould growth within insulation which compromises air quality and materials. Wet insulation also rots wooden structural members through decay.
Structural damageWet insulation adds considerable weight to structures, stressing joints and fasteners. Cycles of wetting and drying also promote insulation settlement which potentially causes air gaps.
Vapour barriers lose effectivenessMoisture saturation stops a vapour barrier's ability to prevent diffusion. This boosts condensation issues within building envelopes.

How much moisture resistance does Celotex offer?

Whether it is an underfloor or roof project, Celotex insulation sets the bar for moisture control. This is because of the superior water resistance of its materials. The closed-cell polyisocyanurate (PIR) foam at the core of Celotex insulation boards does not absorb moisture. 

Water cannot penetrate the cells of the foam, meaning exposure to rain or humidity will not impact thermal performance. Unlike fibreglass and other hygroscopic insulations like sheep’s wool, the PIR foam maintains its structure when wet.

It provides an extremely effective vapour barrier. Water vapour cannot pass through the thickness of the insulation board. Also, the coated glass facers on both sides prevent diffusion. This envelope of moisture protection ensures condensation does not form within building structures.

What thickness of insulation should you use?

Celotex offers boards ranging from 20mm up to 200mm thick. Selecting the right thickness allows you to customise performance for specific building envelope applications.

20-25mm boards for constrained areas

A slim 20-25mm Celotex wall insulation sheet delivers R-value improvements in tight cavities. This includes steel stud walls, curtain wall assemblies and cavity shaft walls. They maximise performance where space is limited.

40-50mm offers excellent all-purpose R-value

This thickness excels at thermally optimising wood frame walls, timber joist ceilings and other common structures. The 40mm-50mm Celotex range also offers superb exterior insulation.

75mm Celotex works with wall cavities

The 75mm Celotex GA4000 fits option works well within 90mm timber stud wall cavities. It can also work for metal stud walls. This allows the insulation to make full contact with framing for improved thermal performance. 

100mm Celotex for maximum thermal performance

For high R-value applications, install thick options such as 100mm-200mm Celotex XR4000 boards. Also, this thickness offers great Celotex external wall insulation on sheathing or over existing walls.

When selecting insulation thickness, it is important to match the board size to the framing cavity depth. This prevents compressed insulation which leaves air pockets that cause condensation and moisture damage to build.

7 top tips for Celotex installation 

Proper installation is key to gaining the full moisture protection benefits of Celotex insulation. Follow these 7 best practice techniques for maximum moisture resistance. 

1. Staggered joints

When installing multiple layers of rigid Celotex boards, stagger all joints between layers. This stops thermal bridging and prevents moisture infiltration.

2. Textured coatings

For exterior continuous insulation, apply special textured coatings to the Celotex insulation board surface. It enhances drainage, drying potential and moisture resistance.

3. Rain screen cladding

Use ventilated and drained rain screen cladding over exterior Celotex insulation. This manages bulk water and boosts the drying of any moisture that gets behind the cladding.

4. Fluid-applied flashing

At openings, transitions and penetrations, install fluid-applied membrane flashings over the Celotex edges. It creates a seamless waterproofing barrier.

5. Penetration spray foam

Seal around all pipe, conduit, wire and duct penetrations through the insulation layer. Use low-expansion spray polyurethane (PU) foam for an airtight and watertight detail.

6. Closed-cell backer rod

Before caulking insulation board joints, insert a closed-cell polyethylene backer rod into the joint gap. This serves as a bond breaker and prevents wetting of the insulation edges.

7. Ventilation above roofing

Providing ventilation above the Celotex insulation boards gives added moisture protection. Strategies like counter-battens on pitched roofs allow airflow to evaporate any moisture.

Proper installation of Celotex insulation with sealed joints and taped edges adds another barrier against moisture issues. The above best practice techniques to install or lay Celotex delivers maximum energy efficiency and durability.

How to maintain Celotex insulation

Proper ongoing maintenance ensures Celotex insulation continues providing maximum moisture protection over decades. Key maintenance principles include the following.

  • Inspect for leaks and repair: Inspect the building envelope annually including joints, penetrations and cladding. Look for signs of bulk water intrusion. Promptly fix any leaks to prevent wetting insulation.
  • Re-seal penetrations: Every 2-3 years, re-seal any joints or penetrations around pipes, electrical boxes, windows and doors. This is because sealants diminish over time. It maintains important vapour and water barriers.
  • Monitor condensation and ventilate: Check the loft and basement spaces for condensation buildup which can wet insulation. This is particularly true for cold and humid months. Ensure proper ventilation per code requirements.
  • Restore damaged vapour barriers: For torn vapour barriers, patch them with rigid insulation material. It prevents moisture diffusion through the insulation layer.
  • Replace wet insulation: Remove water-logged batts or rigid boards within 30 days if they cause condensation or leaks. This will preserve the designed thermal and moisture performance.

Can you use Celotex plasterboard to prevent moisture?

In addition to their insulation products, Celotex manufactures moisture-resistant plasterboard for interior drywall applications. Like insulation, Celotex plasterboard incorporates a PIR foam core to control water.

The foam core creates a vapour barrier that limits diffusion through the plasterboard thickness. This is similar to the low vapour permeance of Celotex rigid insulation.

Celotex plasterboard utilises fibreglass facers vs the foil facings on insulation boards. However, both protect against bulk water damage if installed properly. Similar to insulation, consider the following key points for installation.

  • Install in high-humidity areas like bathrooms, utility rooms and basements.
  • Before installation, ensure proper acclimation to prevent gaps or sagging.
  • Use latex paint for finishing to allow moisture vapour transmission.
  • Tape seams precisely to seal against air and vapour.
  • Seal all penetrations through boards to maintain a vapour barrier.

Shop Celotex boards at competitive trade prices

Building Materials Nationwide proudly supplies a wide selection of moisture-resistant Celotex insulation products. We sell a varied range of dimensions and thicknesses of insulation boards suitable for all project types. 

From Celotex PL4000 to Celotex floor insulation, we have you covered. We provide cost-effective and durable solutions to cut project expenses and boost performance. Plus, we offer quick UK delivery options to meet your project scheduling needs.

If you are a trade customer, open a trade account with us. We offer hassle-free shopping and invoicing of small or large-scale Celotex board orders. Our simple account application process takes a few moments and you can start buying materials straight away.

Our team makes it easy to get the quantities you need when you need them. Contact us today or sign up for a trade account online.

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