Condensation - turn MVHR on early?

[Leaway]

Currently having problems with condensation on the inside of the windows but could be caused by recent plastering. Wondering if to turn the MVHR on early (on extension lead) and would it help?

 

Current situation

Timber frame air tight and sealed, insulation (cellulose) pumped in to the walls and roof.

Triple glazed windows

No electric yet - expect early dec

No heating yet - Expect dec.

Recently plasterboard and freshly skimmed.

Currently juggling logistics with plumbing, tiling, painting to get in part of the house for Christmas.

 

House seems to be getting damper and windows constantly have condensation. Could be the recent plaster but wondering if putting the MVHR on would help?

 

Or would doing that just make things worse by dragging in cold air (currently low 4's outside) and blocking up the filter with plaster dust?

 

Alternatively should i just grin and bare it till mid december?

 

[TerryE]

We are in a similar position. Turning on the MVHR at this stage is a bad idea. You'll just get it and all your piping choked with plaster and other building dust. IMO, just keep the place well ventilated by opening windows and allowing through drafts, so long as the humility isn't fully saturated. Also try a bog standard dehumidifier when it is too damp with windows closed.  This will take out maybe 10ltr per day.

[jfb]

I was lucky to borrow a big dehumidifier in a similar position and it was a big help.

Second the don't turn MVHR on yet.

[PeterW]

I would open windows on opposing sides of the house and get a draft blowing through. To get a dehumidifier working properly you really need a source of heat too, and as most are saying you don't want MVHR on as it will just get full of crud.

[Leaway]

many thanks for the advice i'll stand down from turning on the MVHR just yet and see if i can hire a heat / dehumidifier for the moment

[Ferdinand]

Dehumidifiers are a classic buy and sell don't hire item.

 

A new one will pay for itself in a very small number of weeks in hire charges.

 

Suggest you consider buying something like this Ebac BD70 'secondhand, or the next one up such as a BD150

http://www.appliancesdirect.co.uk/p/1016900/ebac-1016900-dehumidifier?refsource=Apadwords&gclid=COD2reS8vNACFVU_GwodXuUDJg

 

eg

http://www.ebay.co.uk/itm/EBAC-BD70-DUAL-VOLTAGE-INDUSTRIAL-DEHUMIDIFIER-Set-240v-/222319718874?hash=item33c349b1da%3Ag%3At9sAAOSwHMJYMBm9

 

http://www.ebay.co.uk/itm/EBAC-BD150-Dehumidifier-240v-/152320293685?hash=item2376ff3b35:g:FuMAAOSwcUBYLHYv

 

250 to buy, sell for say 150 later, and perhaps 30-40 a week to hire.

 

Ferdinand

 

 

Edited November 22, 2016 by Ferdinand

[TerryE]

As Peter and I both said above, a good old fashion through-draft is better if the R.H. is less than 80% say. 

 

To be honest we just use a standard domestic dehumidifier.  There are plenty to choose from in the £100-150 range, and they cost under a £ / day to run.  IMO, this is fine to take out the moisture from a board skim or paint.  Also handy later if you want to dry clothes indoors.  This would not be man enough, in the case a wet plastered walls, and you'd need the heavyweight sort of dehumidifier that Ferdinand suggests. 

 

Sensus comments re the timber frame don't really apply in the case of a modern passive-style TF, as the VCL is usually on the inner layer and the only inner timber is the joists, floorings and service cavity battening, and these are kiln dried and only expose to the elements for a few days during erection.  Also most self-builds don't work on the accelerated timescales that commercial large-scale developers work to, so the timber, slab, etc have more time to come to equilibrium.

 

What is more of an issue is the moisture content in the floor / slab above the DPC / Radon Barrier.  Our house took about six months for the slab to dry out properly.   You might only have 50-100ltr of water in your plaster skims, but 7m³ of concrete will contain maybe 1+m³ of water or 100× as much!

 

[gravelld]

Maybe get a dessicant dehumidifier, if it's cold inside at the moment?

[TerryE]

@Sensus this discussion is about a house as build not some anonymous worst case.  

 

In our case (TF erected this time last year), the floorboards went direct from the pallet to being fixed in place on the joists.  We had about 2 days of rain in the period before the sarking went on, so the top sealed surfaces did get wet and as the flooring wasn't the waterproof variety, if you now put a steel rule across the floor board joints, then for a few of these,  you can see that there is about 0.5mm blooming / expansion at these joints.  Nothing noticeable from a standing position.

 

The impact in Leaway's case is for him to assess, based on his actual time-line and the weather exposure / damage, surely?  However, if I recall correctly then he also has a similarly constructed MBC frame, so will be in a similar situation to us, and he probably also has a warm slab which involves a lot of concrete being cast on the inside the DPC.

 

As to the humidity point, yes in general for this time of year, but where we live the temperature was ~14°C at midday and the sky was clear just a few days ago, so my advice to use natural ventilation when appropriate still applies.

 

@Leaway, can I suggest that you leave a square of polythene, say 1m square weighted down on your ground floor for a 4-7 days and if the floor gets visibly damp under this, then most of the moisture is still coming from the slab.  As I said, ours took over 6 months to dry out. 

[Stones]

We currently have two industrial dehumidifiers running in our house.  They went on about a week or so before the decorator was due and for the first day or two were pulling out 10 - 15 litres a day each.  Vastly reduced now ( 3 or 4 litres ).

[Ferdinand]

Just to note that when plastering we know the amount of moisture that has gone because it is "x" buckets full that we can count when mixing,

 

Plus body sweat etc.

 

Ferdinand