Positive input Ventilation units – What is your experience?

Positive input Ventilation units – What is your experience?

9:20 AM, 26th November 2024, About 4 weeks ago 46

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Positive input Ventilation units (PIVs) to clear dampness around the window reveals. We have had new double-glazed plastic windows fitted just before the legal requirement of ventilation top vents.

We have super tenants who wipe the windows down daily and understand the need for ventilation and general dampness avoidance.

The plaster around the window reveals shows dampness starting at the top and widening in a triangle to the bottom where they come right out to the inner edge of the windowsill.

My question is, what has been the experience of others who have used the Positive Input ventilation units that sit in the loft and feed a constant trickle of filtered new air into the house below?

I’m talking about the Vent axia units or Pure air or similar. I know some have heaters in them too.

Has anyone fitted aftermarket top ventilators with success?

Your thoughts and experience of their use will be much appreciated.

Thank you.

Mark


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Robert Locke

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10:47 AM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Paul Walters at 27/11/2024 - 09:10
I don't want to hijack a thread that's on PIVs, so I'll be brief.

You want a similar number of air bricks on two different sides of a building with a ventilated subfloor area (preferably opposite sides). The air pressure difference between the two sides of the building forces the air to change under the floor, taking moisture-laden air with it and drying out the sub-floor. If there's a sub-floor wall, this either has a number of airbrick holes in it, or is built in a honeycomb pattern to allow airflow. The number and spacing of airbricks is set out in Building Regulations Approved Document C, section 4.14.

Rising damp is very rare (unless you're a salesperson for a chemical damp proofing company, who probably wants to also sell you a PIV); usually, it's a case of inappropriate materials on an old building, leaking gutters, cement pointing used instead of lime, or ground levels too high and close to the building.

If you'd like to discuss your particular circumstances in more detail, my contact information can be found at http://www.locke.properties

Niwdog

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11:17 AM, 27th November 2024, About 4 weeks ago

My Victorian 3/4 bedroom terraced house had the same tenants for 12 years with never a hint of damp.
New tenants moved in 2 years ago and damp and mould problems started immediately because the heating is barely used and newly washed clothes are dried on the banisters.(On a recent visit the temperature in the house was 13 degrees C.)
So 12 months ago, throughout the house continuously running extractors were installed, wired so that the tenants can't turn them off.
This has been successful and is holding the damp at bay.

Robert Locke

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11:26 AM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Niwdog at 27/11/2024 - 11:17
I've taken to bringing a digital hygrometer with me during inspections, and noting the temperature and relative humidity of each room. Mould spores start to germinate around 65-70% relative humidity, and the lower the temperature is, the greater the relative humidity. If the tenants aren't heating or ventilating adequately, it's a great way to have quantifiable evidence that on that day, at that time, the property wasn't properly heated or ventilated. The same quantity of moisture in the air might be safe and not risking mould at 20°C, but trips over that 65-70% limit when the property isn't adequately heated.

TheMaluka

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12:00 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Niwdog at 27/11/2024 - 11:17
I only heat my own home just enough to stop the pipes freezing, I dry clothes indoors and never have any problems with mould because I ventilate properly, the old-fashioned way, by opening windows. I keep warm with multiple layers of clothing, a heated seat and electric overthrow.

JB

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12:08 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Robert Locke at 27/11/2024 - 11:26
Please can you tell me what hydrometer you use? I have several gadgets for measuring relative humidity and they never agree with each other

JB

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12:10 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Robert Locke at 27/11/2024 - 11:26Do mold spores die when heated or do they fall dormant and reactivate?

Robert Locke

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12:11 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by JB at 27/11/2024 - 12:08
This one: https://amzn.to/3CKGkwa

I live in Reading

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12:21 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Robert Locke at 27/11/2024 - 10:47
Thank you Robert for your thoughts and advice. Including your comments further through the thread.
The building is made of concrete slabs, and of a version I believe to be unmortagable. Possibly a Reema. The walls are impossible to drill into. The floor and all joists are concrete. The more I think about it I need to start with careful examination of the exterior sealing and fit after-market trickle vents.
Much to consider on this thread and thanks to all that have given feedback.

Robert Locke

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12:43 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by JB at 27/11/2024 - 12:10
You'd have to drop the humidity levels uncomfortably low to make mould dormant. Just heating up the room to a normal 20'C isn't going to cut it. The best route is to improve the ventilation and stabilise the humidity around 40-55% R.H., and then use mould cleaners to kill off the growths.

There are mould spores in the air around us all the time; it's just when the growing conditions are right that the formations appear. I'd be more worried about carpets and soft furnishing, particularly if there's been widespread mould.

An ounce of prevention is better than a pound of cure...

Paul Walters

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13:09 PM, 27th November 2024, About 4 weeks ago

Reply to the comment left by Robert Locke at 27/11/2024 - 10:47
Thank you Robert

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