Category: Listed Property News
Dear LPOC,
I have a Grade II listed building. The front part is Georgian and the rear Victorian. The top (2nd floor) whilst Georgian in origin was substantially rebuilt after being bombed in WWII.
As this part of the building has no original features and three outside walls, we have been investigating adding internal insulation to the 11 inch brick walls as we plan to use this floor as offices for our business.
I have read the report into insulating solid walls on the English Heritage website which seems to suggest that internal insulation is not a good idea as it can cause cold bridging and adversely affect the ‘storage heater’ characteristics of the solid walls.
Naturally we do not want to do anything that would adversely affect the building but are keen to reduce heating costs and carbon footprint if at all possible. We have insulated the loft and installed a condensing boiler.
I look forward to hearing from you.
SH
Dear S,
Thank you for your email submitted through the club website.
As always there are pros and cons to everything we do to our buildings and one has to balance the benefits against any potential harms.
There is no doubt that adding insulation to the inside of the walls will reduce heat loss (and carbon emissions) and keep heating bills down.
The downside is that most “dry lining” systems look flat and uninteresting in a historic context, they invariably prevent the ability of the wall to breathe and there is the risk of creating cold bridging which encourages interstitial condensation causing damp and deterioration particularly where there are built in timbers. It can also reduce the thermal mass (the storage heater effect) of the walls although personally I consider this to be a secondary issue.
An alternative which I have seen used in Georgian houses (both historically and recently) is to finish the walls in lath and lime plaster set some 30 or 40mm off the face of the wall. Lime plaster is itself a relatively good thermal insulator and the air cavity is an excellent “free” insulating layer. So long as you use a vapour permeable paint the breathability of the walls is fully maintained and traditional period finishes are restored.
I am also aware that people like Mike Wye and Associates and Chalk Down Lime are experimenting with insulating aggregates (like hemp) in lime mortars. I don’t think figures are yet available to make direct comparison with modern insulating materials but this must be a good way to increase the thermal efficiency of historic houses without compromising their character.
I hope this is of some assistance.
Kind Regards
Peter Bell BA MA IHBC
LPOC Conservation Advisor
Recently published guidance entitled Energy Efficiency and Historic Buildings, Nov 2010 is available at www.english-heritage.org.uk and fully explains all the issues in some depth