Condensation on mdpe pipe in kitchen

[ectoplasmosis]

You'll be gaining a dry pipe!

 

Don't know why it's so difficult to grasp... Just fit the pipe lagging, and stuff a load of mineral wool into the hole until it's flush with the pipe lagging, job done!

[andyscotland]

The air under your house will also be slightly warmer than outside (because it is sheltered and being heated by the house above) and will still have humidity (from the house, and from the ground, and from the outside air).

 

At this time of year, the water pipe itself will likely be colder when water is flowing.

 

So you will potentially get condensation on the MDPE anywhere it is not lagged, but particularly as it gets closer to the house air as the air temperature will rise but the pipe will be the same.

 

With your ideas (taping foil over the top / putting PIR over the top) you are allowing that condensation to form at the top of your floor surface but attempting to seal it there. Hence why your foil was wet underneath. This will eventually be bad for the flooring/structure of the house because that is not designed to be permanently damp.

 

With the pipe lagging solution that everyone else is suggesting, you are *preventing* the warmer air from touching the pipe, so it will not condense in that area.

 

Even if this is only a short length down to just below your joists, that is enough to stop condensation forming where it's a problem.

 

You might still get condensation on the section below the lagging, but this will either evaporate off (due to your subfloor ventilation) or drip onto the solum and eventually evaporate from there. Neither of those is a problem - the solum is expected to be slightly damp at times and the house is designed to accommodate that.

[gambo]

On 22/10/2025 at 12:49, ectoplasmosis said:

You'll be gaining a dry pipe!

 

Don't know why it's so difficult to grasp... Just fit the pipe lagging, and stuff a load of mineral wool into the hole until it's flush with the pipe lagging, job done!

It's not difficul to graspz but i see gaps in what some suggest. I don't see how filling the hole with mineral wool can be any better than covering it with foil+ PIR. Im trying to understand the whole process of forming the condensation to make sure Im bit causing bigger issue later on.

 

[gambo]

@andyscotland wow! That's a great explanation!! Thank you! I'll keep it wrapped (did it a few days ago) a bit longer and will unwrap it just before covering with units to see where and how much if condensation is there, and will give an update.