80% humidity in utility room

[j_s]

Currently renovating the utility room. Half of it is under the detached garage roof (cold roof) and the other half within the house. No heating in there at all apart from what gets through from the 1st floor void and the internal door. The half that was under the garage roof has been completely open/removed since April.

About a month ago a fair few thermalite blocks were replaced when the poorly fitted concrete lintels were corrected. I would say about 18 or so blocks. Heavily dampened by builder to ensure good adhesion of mortar. Various other pointing around soil pipes etc was done. On Thursday the builder finished fixing the block firewall that separates the house from the garage in the loft so it goes up to the roof by adding 10 or so blocks. Again heavily dampened for the mortar. 

 

We've just completed insulating the ceiling with pir board but a day or 2 before I put a humidity and temp digital device to see what low temps we were getting with the more recent lower temps. The temperature was around 10.1c and humidity was 76 or so. Reading it today it is 81 and a temperature of 14.5. Gutters are not leaking, water pipes are all visible and no leaks. Washing machine in the room and door is left open when not in use.  Sink is disconnected and waste pipe is taped up. 

 

I still have to finish sealing up the pir board joins - foaming gaps and cutting out a groove if there is a small gap first. Will then tape all joins. 25mm board will then go under joists and again foam any gaps and tape. Perimeter will be using blowerproof airtight paint between 25mm board and walls. 

 

Nest thermostat in hall says 61% but will rise and fall up to 65. We do have mvhr (utility extract is not setup yet) but the house (built 2007) is renovated and not completely airtight but doing my best to do so.  When outside air dries a bit more then humidity sits at 52/53 during the winter. Summer is around the same or slightly higher at 55 ish but obviously fluctuates. 

 

Could it still be drying out in the utility room or is there something hidden that could be causing the much higher humidity? The concern being the stark difference between the hallway and utility room. 

 

 

Edited November 26, 2022 by j_s

[SteamyTea]

Keep track of the numbers, get some data from a local WeatherUnderground station, and run them though this calculator.  You may find they are quite normal for this time of year.

 

[j_s]

86% outside humidity and 11c outside. 

Not quite sure on the calculator though which is a tad embarrassing. 

[S2D2]

1 hour ago, j_s said:

86% outside humidity and 11c outside. 

Not quite sure on the calculator though which is a tad embarrassing. 

The idea being (I think) you can convert the outside air to absolute humidity then calculate the relative humidity once you have raised it to internal temperatures. This gives you a "best case" relative humidity if you were to add no moisture at all. I think in your case it comes out at 72%, you are adding 9pp from somewhere which seems perfectly within the bounds of evaporating construction moisture or even just general household usage. Heat the room or run a dehumidifier and it will stabilise. I've been looking at this on our house and we were sitting about 13pp above best case humidity due to drying clothes etc. Dehumidifier reduced it down to 55% within a week.

[MJNewton]

1 hour ago, j_s said:

86% outside humidity and 11c outside. 

Not quite sure on the calculator though which is a tad embarrassing. 

 

There's a simpler calculator here - just enter the outside temperature, outside humidity and inside temperature and it'll tell you the resulting inside humidity (assuming no additional moisture or dehumidification taking place as S2D2 says).

[j_s]

Cheers all 🙂