Conservatory with no cavity tray and blocked air bricks

Antill & Co. Chartered Surveyors carried out a RICS Home Survey Level 3 (RICS Building Survey) on behalf of a client purchasing a four-bedroom detached house, built in 2020, located in Emsworth, Hampshire, PO10.

The survey highlighted several defects as a result of the current owner’s alterations to this new build property, one being the addition of a conservatory without installing a cavity tray to the outer leaf of brickwork above it and blocking the air bricks of the existing part of the house.

There was no evidence of a cavity tray above the conservatory. Cavity trays are required to be inserted above an extension to prevent moisture penetrating through the exterior brickwork above the extension down the wall into the interior of the extension.

Before the conservatory was added, there was no need for a cavity tray as the wall was an external wall, however now it is an internal wall between the conservatory, the kitchen and the sitting room. Without a cavity tray, there is a risk of rainwater penetrating through external brickwork, running into the cavity and soaking the internal wall between the conservatory and the kitchen and sitting room walls.

Image courtesy of NHBC/Standards

We recommended that a cavity tray must be fitted to minimise the risk of rainwater ingress. This will be costly, and access will be difficult. The cost to rectify this issue is estimated to be in the region of £5,000.

The original cavity trays located above the patio doors from the kitchen and sitting room and the window of the kitchen have been built over by the conservatory. Should rainwater enter the cavity, it will now drain out of the weep holes into the conservatory rather than draining to the outside. (NB: a weep hole is a small opening that allows rainwater to drain out of the lintels above the windows and external doors to the outside) This is again why it is important that the conservatory should have its own independent cavity tray.

Additionally, the conservatory blocks the air bricks to the rear elevation of the original part of the house. Air bricks are designed to provide ventilation to the sub floor void and minimise the build-up of radon and methane gas. Blocking the air bricks therefore presents a safety risk.  Air bricks should have been installed to the rear elevation of the conservatory that connect to the air bricks of the main house via ducting. Installing air bricks now will be costly and access will be difficult as the suspended floor of the conservatory requires removal. The cost of rectifying this issue is estimated to be in the region of £2,000.

The issues raised above compromise building regulation compliance of the original house. Furthermore, given that the house is less than 10 years old and is still under NHBC warranty, these issues may invalidate the warranty if dampness problems arise as a result of these non-compliant alterations.

The RICS Home Survey Level 3 highlighted £7,000 of remedial costs on these issues alone that our client would have otherwise been unaware of prior to purchase. This valuable insight provided our client with the opportunity to revise the purchase price of the property prior to exchange of contracts and avoided the discovery of costly issues after moving in. Forewarned is certainly forearmed.