1. Hi Matt, no it wont weaken the seal. You will need to ensure that the opening is sealed well and that the cut edges are painted to protect from corrosion. It is the same process as if you were extracting through a brick wall but the steel is easier to cut providing you use the right cutting tool. You need to make sure that you place the cut on a flat section of the steel and not on an area that has the raised box profile. i.e don’t cut through the vertical ridged section that you can see from outside.

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        1. I’ve not undertaken a soffit extraction myself Matt but I don’t see why it wouldn’t work as long as the soffit area is sound as they do tend to suffer from corrosion near the corners of the house.
          The image below, although not relating to a bisf house depicts the vent. It is imperative that all pipe vents are well sealed from the extractor pipe to the vent outlet as you do not want any moisture entering the loft space as this could aid corrosion.
          It shouldn’t be difficult though. :0)

  1. My neighbours have used the vent on the roof that originally vented the vent (stench) pipe from the toilet after they had removed that pipe and replaced it with an air inlet valve.

    I’m thinking of something similar, but I’m planning a small mechanical heat recovery ventilation system at the moment to extract air from the bathroom and kitchen and supply it to the bedroom and living room. The heat recovery means that most of the heat from the extracted air is put back into the cold air coming in so you don’t lose your expensive heating nearly as much through ventilation. Also, by lowering the humidity in the house in general it will combat the risk of any condensation and corrosion of the steel frame.

    The plan at the moment is to mount the unit in the loft to extract/intake at roof level and then have inlet vents in the bathroom and kitchen ceilings and outlet vents in the front bedroom and living room ceilings. I would put the ducts from the loft to the the living room through the built-in cupboards in between the two main bedrooms and the one to the kitchen in the bathroom wall behind the bath when I reboard it (water leaking has soaked the plasterboard). This will involve making the wall very slightly thicker to accommodate 204 x 60mm flat PVC duct.

    That’s the plan anyway!