Exterior Insulation is the most practical and effective solution for old houses. Ballytherm insulation boards are a high-quality product intended for this job. Described as High Performance PIR Wall Insulation Slabs, they are a thermoset plastic material moulded into a rigid thermal insulation board.
Wall Insulation Slabs are designed to prevent water seepage through walls. Ballytherm highlight different types of moisture problem to bear in mind:
1. Walls need to have a good DPC, in turn connected to any DPM, to stop the rise of moisture from the soil. If there is a radon barrier, this must run through to the outside face of the exterior wall. Use pre-formed cavity trays, sealed to the radon barrier inside the cavity, to do this. To avoid forming a slip plane between membranes, do not set both the DPC and radon barrier in one mortar joint.
2. Wind-driven rain on exterior surfaces can creep through to the interior. The critical factors here are: a) the severity of the weather; b) the surface texture and jointing; and c) the insulation type and location. The ultra-low thermal resistance of Ballytherm insulation boarding means a wall, plus residual cavity, will not appear significantly thicker, whilst still achieving a good thermal performance.
3. As warm water vapour passes through from the interior, it can condense inside the wall. To prevent this, a vapour control zone can be created below the plasterboard by using Ballytherm foil-faced boards and a metalised tape seal at each joint.
Eliminating thermal bridging at the wall/roof interface can be tricky. With ‘cold’ insulation around the ceiling joists, use fibrous insulation forced between the rafters to reach all the way to the wall head. For rigid, ‘warm’ insulation on the rafters, Ballytherm boarding can be taken from the wall head to the insulation up above.
Windows and doors should be inset and well-detailed to ensure a good insulation seal.
Use smaller stainless steel, or plastic, ties and fixings to minimise the negative effects on thermal performance.
Heating flues must be sleeved, or a combination flue used, to prevent any contact with the insulation.