Attic condensation - Droplets on the felt

Do not replace the insulation.

If the Condensation on the felt is now eliminated, it means the ventilation of the attic void is adequate.

With the is ventilation - the moisture in the rafters will dry out. The rafters cannot get attacked by Wet Rot or Dry Rot.

It is unbelievable the amount of houses where some Plonker exhausted the moisture, with a fan, from a Bathroom/ Shower Room up in to the Attic void. Human Stupidly knows no bounds.

Loads of advice here:

https://www.google.com/search?q=site%3Aboards.ie+on+felt+condensation

Yes, there would be in newer builds since about 20 years ago. There is a vapour control foil commonly included in plasterboards (foil-backed) but the plastic sheeting (VCL) is also applied to seal between the joints, etc, but it's not easy to retro-fit except where there is a deep refurb going on.

Like this if you view it from the attic.

But nonetheless, do have a read of the other links provided above as the typical treatment of attic condensation is well documented on this forum.

I would not be worried about a Vapour Barrier (VP) ( which must always be on the warm side of the insulation).

If the lack of a VP was a problem then it would result in Interstitial Condensation- within the Insulation.

Your problem is Surface Condensation on the felt

Your insulation is perfect - it is reducing the heat loss from the living rooms, and therefore it is very cold in the Attic Void. This is the function of the Thermal Insulation.

Adding more insulation will allow less heat loss to escape in to the attic void, which will reduce your heating costs of the house. This will make the attic void colder and cause more Surface Condensation.

You need to find the cause of the moisture in the attic void which is causing the surface condensation on the underside of the felt.

There are 2 reasons for this surface condensation.

Readon 1

1. Moisture from the dwelling escaping in to the attic
2. This could be caused by extractor fans exhaustion steam/ moisture from Bathrooms or Kitchen in to the attic void. ( Yes some Plonkers do this).
3. Moisture escaping from the dwelling in to the attic void through holes in the ceiling of the Hot Press, and through gaps in the Attic Access door and through small holes in the ceilings where the wires of the ceiling lights pass through the ceiling slab.
4. You must seal all of these gaps. I would use Mastic to fill these gaps.
5. Fit Draught Excluder strips on the Attic Access Door.

Reason 2ack of Ventilation in the Attic Void

Surface Condensation on the underside of the felt is generally caused by a lack of Through Ventilation of the Attic Void - vents in the Soffit at the front of the house and also at the rear of the house. Therefore to solve the problem to prevent the surface Condensation of the felt- you need to fit plenty of Soffit vents - back and front.

If you do not know how to do this- let me know.

Your family friend did not give you correct unbiased advice.

You received biased advice from a Salesperson who only wishes to take money from you.

Here is free, unbiased, professional advice from a stranger.

Ignore what your friend advised.

Your Attis has a lack of Through Ventilation.

The fact that there is condensation forming on the underside of the felt, indicates that the Attic Void is cold, which means that your Ceiling Insulation is functioning correctly.

You need to provide Through Ventilation to you attic void.

Here is a Diagram from Technical Guidance Document F of the Building Regulations.

If you comply with this it will eliminate the surface condensation in the Attic Void.

From this diagram you can see the ventilation area required at both sides of the roof is an area - the length of the roof x 10 mm.

Say you roof is 12 m long.

For each side:- 12,000 mm x 10 mm = 120,000 mm2.

Assume each PVC round vent gives 2,500 mm2

120,000 mm2 divided x 2,500 mm2 = 48 circular vents at each side.

A Carpenter Joiner could fit vents in the soffit for you.

A soffit and fascia fitter could fit soffit vents for you.

You could fit any types of recommend vents available, but the following 2 photos show PVC Circular vents, which are simply to fit.

wow some levels of incompetence, laziness and indifference displayed there from multiple different installers and so called professionals. Goes to show if you want anything done correctly you have to do it yourself.

Good looking plan above and in relation to point 6 depending on what sort of access you have with a loft ladder, stira etc an insulated hatch cover (something like the below) could work well. If just a straightforward hatch with no attached ladder or other obstacles then it's much easier insulate with some PIR board.

Let us know if you get easy and reasonably priced vent trays as in point 3. I looked for these a couple of years ago and were difficult to source and very expensive. Good thread here on that matter which might be of interest:

What a Plonker of an Electrician to pump Steam from the Bath/ Shower in to the Attic Void. It’s not unbelievable as I seen it in many houses. It must be exhausted to the external air.

Soffit and Fascia Experts - PVC Vents going nowhere. A bunch of Langers. I have also seen this on many houses.

The builder was another Plonker not to exhaust the bathroom vent duct out through the soffit to the external atmosphere.

The Construction Industry is full of totally incompetent morans.

finnyob

My advice on the following as you have listed above:-

1. Yes
2. Get the Bathroom steam out of the attic void immediately.
3. No. Waste of time and money. Push insulation down approximately 40 mm from felt at eaves to allow through ventilation flow from one side of the attic to the other side.
4. Yes. Fill with mastic - all holes around wires of ceiling lights, holes around pipes in ceiling of Hot Press and all pipes passing through the ceiling. Seal around attic access door.
5. See sketch- below. Insulate around and above the water tank with rigid insulation. No insulation under the tank.
6. Yes. And stick 100 mm high density insulation on top of the trapdoor with mastic.
7. No. Not necessary.
8. No. Not necessary.

Good shout @C. Eastwood, thanks very much. I suppose just on the eaves vent trays, I'll probably still go with them as they would guarantee that the insulation can't block up airflow. Our attic is very awkward, 25deg slope so access to eaves is difficult for a tall chap like me. The Klober ones I have seen are 20quid per pack of 10 from a supplier in Ballymount, so I think it's worth it for the 60 quid I'd spend.