How to Insulate a Corrugated Roof

Insulation, Membranes & Felts
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How to Insulate a Corrugated Roof

Metal roofing sheets are a popular and commonly spotted roofing material across the UK. Their robust structure and resilient strength make them the perfect choice for heavy duty structures, offering optimum durability and weatherproofing. Metal roofs are relatively affordable, pretty easy to install and low maintenance so are a practical choice for a multitude of building structures.

But when it comes to insulation, is metal any good? Despite its many practical features, metal roofing can provide relatively poor thermal insulative properties in comparison to many other material alternatives.

To maximise the efficiency of your metal roofing, it is a good idea to invest in some high-quality roof insulation to keep the building below at a comfortable and consistent temperature all year round. In this article, we will discuss the benefits of insulating your metal roof, the most common types on the market as well as step-by-step installation guide for each.

Benefits of Metal Roof Insulation

Environmental Impact

The colder the building below, the more energy you will use to heat it. With the addition of insulative materials, you can significantly lessen the need for this energy use and reduce the level of air pollution produced. This will help to bring down your carbon footprint and minimise emissions, creating less of a negative impact on the environment.

Reduced Costs

When a roofing structure is left uninsulated, a significant amount of heat and energy will be lost. This not only has a negative effect on the environment but can also have a major impact on how much you are spending on utility costs each year. With the effective use of high-quality insulative materials, you can significantly cut down on just how much money you are spending annually on heating, plus can often even pay off the insulation costs within just a few years.

Increased Value

Surprisingly, simply adding installation to a roof structure can add a significant amount of value to the building. The more energy efficient the building, the higher it will be rated in terms of value. More people will be interested in a property if it can maintain a high level of comfort inside with less pricey running costs.  

Acoustic Absorption

Metal roofs can be pretty noisy, especially in adverse weather conditions. This is where insulation can make a difference. Not only is insulation designed to provide thermal protection, but it can also absorb sounds and reduce noise transfer, creating a quieter, more relaxed environment in the building below.

Better Comfort

Insulating your metal roof structure will help to regulate temperature and create a far more comfortable temperature throughout the building. Some metal roofing materials can get pretty warm in the summer which creates an uncomfortable heat inside. Insulation will not only help to maintain warmth throughout the chilly winter months but will also help to cool down the building when it’s that little bit too hot.

Enhanced Protection

Although metal roofing is generally very robust, adding a layer of insulation will also act as an additional layer of protection, enhancing durability further. Without adequately insulating your roof structure, rising heat can lead to melting snow and ice in the winter. This can then lead to ice dams, condensation and moisture which may cause potential damage to the roof.

What Options Do I Have?

When it comes to insulating a metal roof, you have a few options of which kind you can use. Each offer its own selection of benefits and features that make them best suited to varying purposes. Here are a few of the most common insulating materials for metal corrugated roofing:

Rigid Foam Insulation

Rigid foam insulation, also known as a foam board or rigid board insulation, is available in both sheets and panels. It is most commonly manufactured from polystyrene, polyiso and polyurethane.

The chemical structure of rigid foam is “closed cell”, whereas many insulative materials are “open cell”. Closed cell insulators typically provide superior durability, strength and resilience, whilst offering a higher average R-value. This higher R-value means better resistance against flow of heat well so better insulation for the roof structure. (source: buildwithrise) When the foam sheets are fitted together tightly with the joints caulked/sealed, rigid foam offers fantastic thermal resistance.

Rigid foam insulation is a popular choice for corrugated metal roofs as it is far denser and thicker. This means it can be easily installed with fewer joints and gaps, in turn minimising air leakage. It provides excellent water resistance and with correct installation, could last for up to 100 years. (source: buildwithrise)

Something to consider when using rigid foam insulation is that UV rays can cause damage to the structure and it must be fitted tightly to prevent air infiltration. This is why it is so vital that the boards or panels are fitted correctly.

Spray Foam

Spray foam is a highly versatile insulative material that can be used in your roof, loft, walls and floor. It comes in the form of a liquid foam which is carefully sprayed into the correct position through high-pressure spray equipment. As the foam reacts with the air, it expands, hardens and cures within just minutes, creating a durable thick and rigid foam layer.

Insulating a corrugated metal roof can seem pretty tricky. However with spray foam insulation the process is far quicker and easier thanks to its practical workability. It is completely self-adhering so it is ideal for the awkward shapes of corrugated roofing plus can be used on both old and new metal roofing.

Significantly reducing the risks of condensation and moisture damage, spray foam insulation fits so tightly into small cracks and crevices that after swelling and drying, it completely blocks out water and air. This tight fit also prevents the entry of pollen and allergens as well as insects, bugs, and small rodents.

As well as being a fantastic thermal insulator, spray foam also helps to minimise noise. Open cell spray foam insulation is one of the best materials for blocking out unwanted sounds so is perfect if the building is situated in a busy, built-up area.

Fibreglass Batts

One of the most affordable and practical insulators for metal roofing, fibreglass batts are budget-friendly and versatile. They can be cut easily to accommodate the shape and size of your roof structure, so are perfect for tricky corrugated profiles. Fibreglass batts are comprised of fine, threadlike-glass formations which are woven together and mixed with various other materials to create a thick, robust insulating pad. (source: legacyusa)

Often fibreglass batts are made from recycled glass, which provides great environmental benefits. The structure is robust and resilient so will not collapse easily, plus offers resistant to fire to enhance the safety of the building structure.

In terms of insulative performance, fibreglass slab insulation is very effective in increasing the energy efficiency of your home. The structure of the material traps pockets of air to slow the spread of heat and cold, keeping the building warm in the winter and cool in the summer. As well as thermal insulation, fibreglass also helps to minimise the level of noise that travels from the outside in, creating a more productive and comfortable environment.

Although fibreglass batts are generally pretty easy to install, they can be unsafe when handled by an inexperienced user. As the structure contains microscopic glass pieces, you must always ensure that you wear appropriate PPE including goggles, gloves and dust mask when fitting.

How to Insulate a Corrugated Metal Roof

Fibreglass Batts & Rigid Foam – Existing Structure

  1. Inspect the Underside

When inspecting the underside of your existing structure, you should see existing plywood horizontal beams and larger angled beams called joists.

  1. Fit Fibreglass Batts into Gaps

To begin insulating the existing structure, start by placing fibreglass batts into the gaps between the horizontal beams and the roof decking. Don’t fit the fibreglass too compacted as this could hinder the performance of the material. Fitting as loosely as possible into the gaps will be more effective.

  1. Coverage with Rigid Foam

Next, use rigid foam insulation to provide a wider span of coverage for the roof decking between the joists. You can cut the sheets to size using a utility knife and then simply secure into place using staples or an appropriate adhesive.

It is advised that you don’t use nails/screws as these types of fixings may penetrate through the metal roof sheets and cause leakages.

Rigid Foam in a New Structure

  1. Install the Roof Decking

To create the structural roof decking, it is recommended that you use either plywood or OSB boards. Lay the plywood or OSB vertical to the joists, then secure into position using galvanised or stainless steel roofing nails.

  1. Fit Roofing Membrane

Fit a layer of roofing membrane over the decking to minimise the risk of moisture damage and leakages. Fasten the roofing membrane securely using either nails or staples.

  1. Secure Rigid Foam

Fit rigid foam sheets over the membrane across the whole roof surface. Ensure that the insulation sheets are closely butted together, but not overlapping.

  1. Seal the Beams

Using a strong duct tape, carefully seal the beams in between the rigid foam insulation sheets. This will help to minimise moisture, protect against air leakages and enhance the structural stability and strength of the roof.

  1. Install the Metal Roofing Sheets

Now the insulation is in place, you are ready to fit the metal roofing sheets over the top. Make sure to stick to the specific manufacturer’s instructions.

Spray Foam Installation

  1. Where to Find

If you are DIYing your spray foam installation, it is recommended that you purchase a ready set up spray foam insulation kit. This should include a sprayer and closed-cell liquid foam. If you are unsure on whether your kit is correct for use, always ask a professional for advice before installation.

  1. Cut a Hole

To begin, you will first need to cut a small hole in the ceiling. This will provide easy access to the roof framing. If you are unsure on what the size of the hole should be, refer to the manufacturers installation guide that should be available with your spray foam kit. This should tell you the correct size for the hole as well as positioning.

  1. Double-check the Structure

Before spraying, you need to ensure that your metal roof is adequately supported by either plywood or OSB board roof decking. If you find that your metal roof does not have this installed beneath the sheets, you should not attempt the DIY installation of the spray foam. This is because the foam could move through the roof seams and cause major structural damage.
Always ask a professional for advise if you find that your metal roof does not have the appropriate roof decking support and do not continue on your own.

  1. Spray into the Hole

If after inspecting, you have confirmed that your metal roof has the plywood or OSB beneath, you can initiate the spray foam installation. Spray the foam carefully into the hole created earlier. Make sure to closely follow the manufacturer’s instructions and guidance.

Once sprayed, the foam will begin to expand, filling the roof structure. Once fully expanded, hardened and cured, patch up the hole to finish.

To Conclude

Corrugated roof sheets are a popular choice all over the UK for a multitude of different building structures. From their practicality and strength to their unique visual appeal and versatility, corrugated sheets are a highly effective roofing solution that are perfect for a DIY project.

Choosing and installing the right insulative material will help to maximise and enhance this top-quality performance. Here at Roofing Megastore, we offer a cost-effective, high-quality range of insulation from boards, rolls and slabs to multifoil and even natural insulation.

If you have any further questions or queries, don’t hesitate to get in touch with our friendly customer service team who will be more than happy to help. Simply give them a call on 01295 565565, email [email protected], or leave a message in our handy live chat.

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