Under Building Regulations 2010, corridor walls adjacent to dwellings can be classed as:
a) A sheltered wall, if the adjacent corridor is unheated
b) A party wall, if the adjacent corridor is heated
The u-value of a wall separating a dwelling with an unheated corridor must be considered as a ‘heat loss wall’ under Criteria 2 Guidance of Part L. The area weighted limiting u-value for all heat loss walls in a dwelling must not exceed 0.30W/m2K under Part L 2010. Therefore, if a sheltered wall makes up a significant proportion of the total heat loss wall area of a dwelling, it must be insulated to standards that ensure the total heat loss wall area meets or surpasses the 0.30W/m2K limiting u-value.
A wall separating a dwelling with a heated corridor must be considered as a ‘party wall’. Under Part L 2010, the limiting u-value for a party wall is 0.20W/m2k. However, the u-value is not calculated in the conventional way; rather the following default u-values are used in certain scenarios:
Since the default u-value of an unfilled cavity in a party wall does not meet the limiting u-value, filling the cavity is a requirement. However, the extent of insulation bears no relevance.
We have been examining this issue because insulating corridor walls is often overlooked and it is becoming increasingly important as Building Regulations grow more demanding. Here is our suggested course of action for insulation.
Anecdotal evidence has shown that, in a number of circumstances, corridors that are technically ‘heated corridors’ are overheating in the summer, particularly where a communal area (e.g. landing) is surrounded by dwellings. This is often a result of heat being added through transient pipes on communally heated schemes. Furthermore, lighting in corridors is also being blamed for the problem. The issue has resulted in some designers actually adapting fire strategies to ventilate corridors.
Therefore, there is an argument for ventilating and cooling corridors, rather than heating them.
Should we fully insulate corridor walls next to dwellings?
Following an internal technical workshop, we have come to the view that it is more favourable to fully insulate walls between communal areas and dwellings, treating them as you would an external heat loss wall. This is the more favoured option for a number of reasons:
- To avoid/reduce the risk of overheating in communal areas such as stairwells and corridors.
- To ensure maximum Fabric Energy Efficiency (FEE) scores are obtained, currently relevant to the Code for Sustainable Homes, but soon to be integrated into Part L 2012/13 Building Regulations. [Refer to our Part L energy efficiency article for further details].
- To ensure dwellings are properly insulated and give full control to residents over heating their homes.