To insulate a roof from the inside, especially for traditional pitched roofs, you typically focus on methods applied between or onto the roof timbers (joists or rafters).
For traditional pitched roofs, sometimes called sloping roofs, you will be looking at three main options to insulate from the inside:
Main Methods for Insulating Pitched Roofs from the Inside
Insulating from the interior involves working within the attic space, installing materials between or against the roof rafters. This is a common method, particularly when the roof covering is not being replaced.
Here are the primary techniques mentioned in the reference:
1. Installing Solid Insulation Boards Between the Joists
This method involves cutting rigid insulation boards (such as PIR or phenolic foam) to fit snugly between the roof rafters.
- Process: Boards are measured, cut precisely, and friction-fitted or secured between the rafters. Gaps around the boards should be sealed with expanding foam or tape to prevent air leakage.
- Benefits: Provides excellent thermal performance per thickness, resistant to moisture, and relatively easy to handle and cut.
- Considerations: Requires careful cutting and fitting to avoid gaps. Can reduce headroom if installed below the rafters as well.
2. Installing Fibreglass or Mineral Wool Insulation Batts Within the Joists
This is a common and often cost-effective method using flexible rolls or batts made from materials like fibreglass or mineral wool.
- Process: Rolls or batts are cut to size and placed between the rafters. It's crucial that they are installed without compression to maintain their insulating properties. A breathable membrane or ventilation gap may be required above the insulation depending on the roof structure and ventilation strategy.
- Benefits: Relatively inexpensive, widely available, and flexible, making them easier to fit around irregular spaces.
- Considerations: Requires careful handling (especially fibreglass) and proper ventilation to prevent moisture issues. Must be installed without gaps or compression.
3. Installing Spray Foam Insulation
Spray foam insulation, typically polyurethane, is applied directly onto the underside of the roof deck or between the rafters.
- Types:
- Open-cell spray foam: More flexible and vapour-permeable.
- Closed-cell spray foam: Denser, provides a vapour barrier, and adds structural strength.
- Process: Applied using specialized equipment, the foam expands to fill cavities and create a tight seal.
- Benefits: Creates an excellent airtight barrier, conforms to irregular shapes, and closed-cell foam can add structural rigidity.
- Considerations: Requires professional installation due to the equipment and chemicals involved. Ventilation requirements must be carefully considered, especially with closed-cell foam applied directly to the roof deck.
Summary Table
| Method | Material Type | Installation | Key Benefits | Considerations |
|---|---|---|---|---|
| Solid Insulation Boards | PIR, Phenolic Foam | Cut and fit between rafters | High thermal performance, moisture resistant | Precise cutting needed, gap sealing crucial |
| Fibreglass/Mineral Wool | Fibreglass, Mineral Wool | Place batts between rafters | Cost-effective, flexible | Requires ventilation, must avoid compression |
| Spray Foam Insulation | Polyurethane (Open/Closed) | Sprayed onto roof deck/rafters | Airtight seal, conforms to shapes | Professional installation needed, ventilation key |
Choosing the best method depends on factors such as budget, the complexity of the roof structure, desired R-value (insulation level), and whether you are comfortable with DIY or prefer professional installation. Proper ventilation is critical for all methods to prevent moisture build-up and potential issues like rot or mould.
