My builder "forgot" to apply polythene sheet vapour barrier around (on the inside) of internal insulation (foil backed) with timber batons. A recalculation of the condensation risk (without the poleythene sheet vapour barrier), shows only minimal condensation at the worst time of the year, with no annual moisture accumulation. However, they still regard it as not recommended.
I'm thinking about what could go wrong if I apply vapour seal liquid (DryBase) to the walls to try and compensate for the missing sheet. I would also be vapour taping all gaps, including sockets. Most of the floor will be sealed as is usual. What I won't be covering with this approach are the edges of the floor (which are under the plasterboard so are not accessible).
Since, according to the updated calculation, there will only be minimal condensation with the current state of things, is it worth the risk of applying the liquid DPM, or should I be safe and improve things with my approach? Three issues I can think of are:
- Moisture trapped in plasterboard between the foil and liquid DPM.
- More vapour coming through at floor level than previously, since less routes of escape.
- Somewhat related to the last point. It will be more difficult for any condensation collected in the floor inside the walls to escape (since most of the internals will be sealed).
How significant are these? For the first I would need to ensure no sudden cooling of the house. For the second one I would need to ensure there is adequate ventilation inside the house. I'm not sure about the floor though but feel that the net effect should be less vapour flow.
Is there anything else I need to consider? Is it worth also considering adding a vent from the timber baton cavity? Should I speak to an architect?
I'm thinking about what could go wrong if I apply vapour seal liquid (DryBase) to the walls to try and compensate for the missing sheet. I would also be vapour taping all gaps, including sockets. Most of the floor will be sealed as is usual. What I won't be covering with this approach are the edges of the floor (which are under the plasterboard so are not accessible).
Since, according to the updated calculation, there will only be minimal condensation with the current state of things, is it worth the risk of applying the liquid DPM, or should I be safe and improve things with my approach? Three issues I can think of are:
- Moisture trapped in plasterboard between the foil and liquid DPM.
- More vapour coming through at floor level than previously, since less routes of escape.
- Somewhat related to the last point. It will be more difficult for any condensation collected in the floor inside the walls to escape (since most of the internals will be sealed).
How significant are these? For the first I would need to ensure no sudden cooling of the house. For the second one I would need to ensure there is adequate ventilation inside the house. I'm not sure about the floor though but feel that the net effect should be less vapour flow.
Is there anything else I need to consider? Is it worth also considering adding a vent from the timber baton cavity? Should I speak to an architect?
