What to check before cutting vents into soffit


Postby Ian Dudley » Thu Sep 16, 2010 9:24 am

My 1920's detched house has a pretty bad condensation problem throughout. It looks like previous owners were over-enthusiastic with insulation and we get lots of surface damp/mold problems in the less travelled parts of the house, and need to run a dehumidifyer all the time through the colder weather.

I'm doing a bunch of projects to try and fix this, one of which is to look at the loft. We don't get mold up there, but there has been enough condensation for it to drip off the joists in sufficient quantity to soak boxes stored up there and stain some stuff.

Looking around, I can't see any evidence of vents in the walls, peak or roof tiles. The soffits run the length of the house and there are definitely no vents there on either side.

Internally, the loft has patchy fibreglass insulation and loose boarding (pretty poor quality DIY job from the looks of it). One end of the loft has a large semi-circular window (an odd feature as the roof is way too low to use it as a room), but it doesn't open and there aren't any vents in there either. There's also the cold water tank (no lid, need to fix that) and a header tank for the CH.

Our neighbour in a similar built house has soffit vents, so I suspect that is what I should have. But is there anything else I should check or do before getting busy with the hole saw? I've got the ladders I'll need and plan to get 70mm circular vents, probably 8 a side or something like that.

It looks pretty straightforward, but not being a roofing expert I just want to make sure I'm on the right path before cutting lots of holes in stuff! Any advice or pointers appreciated.
Ian Dudley
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Joined: Fri Dec 05, 2008 11:18 am

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Postby Perry525 » Tue Sep 21, 2010 7:48 pm

Condensation is caused by washing, cooking, breathing, sweating!
When your home was built, it was designed to be cold and drafty!
Open fires dragged cold air through every hole and crack, keeping the place cold and dry.
As you write, the previous owners, sealed holes and insulated and in so doing upset the balance.

What you need, is to deal with the water vapour you are creating by venting it to the outside.

You can open windows.
You can install a forced ventilation system.
You can install extractor fans in the kitchen and bathroom.
You can buy and use a larger de humidifier.

Most of the time the air outside is colder and drier, that the air inside that is warmer and wetter.

As water vapour prefers cold, it will most of the time move outside if you let it, not always, as some of the time the air outside is roughly the same temperature and humidity as the inside.

However, you are troubled during the winter, when you are keeping the doors and windows closed to save on heating and in so doing trapping the water vapour indoors.

The de humidifier solution is the best from the point of conserving heat, it helps by removing the water vapour and at the same time adding heat to the home.

Dry air is cheaper to heat than wet air.
But you do need some fresh air.
Extractor fans, complete with heat exchangers, timers and humidistats are favorite, they will remove the water vapour and warm the in comming air saving perhaps 80 to 90% of your heat.

Take a look at the upstairs ceilings, block every hole and crack, make sure the entrance to the loft is air tight, try to stop the water vapour having easy access.

Note: Water vapour is a gas that can and does move through most things, ceiling plasterboard is transparent to water vapour, covering with a gloss almost water vapour proof paint will help stop it entering your loft.

Increasing the insulation, will help remove the attractiveness of the cold loft.
Perry525
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Joined: Fri Jul 06, 2007 7:35 pm


Postby Ian Dudley » Mon Sep 27, 2010 2:36 pm

Thanks for the reply. I'm aware of the general causes of condensation and am doing a range of projects to address this, including an extractor fan in the bathroom (using an existing vent someone plastered over!), cupboard vents, air bricks to the less travelled rooms, etc. ultimately I'll probably get new windows fitted with trickle vents, as the current ones are all in pretty poor condition anyway, but that's quite an expense.

With regards the loft, unfortunately the previous owners had a real thing for spotlights, so there are holes cut through to the loft space in a number of places, and it's a pretty big job to fix them. We'd really need to replace the spots with pendant lights (which we'd like to anyway), but then we have to think about re-doing the ceilings, which are all horrid textured Artex (maybe with Asbestos?), so it quickly becomes a pretty big job.

Also, from what I understand it's fairly normal practise to have vents of some decription in the loft space, even if you have managed to keep the insulation pretty tight. As you say the water vapour will penetrate most things and get up there, so it needs a way to get out.

I've looked carefully all round the loft, both inside and out, and there are no vents anywhere at all, the loft is completely sealed. Not fancying chopping bricks out for a vent or messing about with the roof itself, soffit vents seem to be a pretty simple option here. I can get a hole saw and a couple of packs of vents for less than a tenner on Screwfix, I already own the ladders and can see there is plenty of space on the soffits themselves, so it's looks like a pretty straightforward job. Up the ladder, zap a hole with the saw, push in a vent. Rinse, repeat.

I just want to check if there is anything else I should check before getting busy with the saw. I'm going to have a good look about the inside (as much as is possible in such a restricted space), as I don't want to be zapping holes into a mains cable or water pipe. Is there anything else I should be checking?
Ian Dudley
Posts: 8
Joined: Fri Dec 05, 2008 11:18 am


Postby Perry525 » Tue Sep 28, 2010 11:08 am

Air bricks are not a good idea, they are old technology that has been discredited.
The problem are, they are open all the time,
a different heights and exposures above ground they provide different amounts of ventilation, dependent on the pressure of the wind, they are in practice un controllable, they let warm expensive heat out.
Making un used room even colder is not a good idea.
Trickle vents are banned for the same reason!

From 2016 all new houses will have to be of Passive House standard.....this means air tight!
With controlled ventilation.
This is to save on heating costs etc;

You can draw the hole size on a piece of cardboard, transfer it to a piece of plasterboard, cut the plasterboard to size and holding a piece of wood in place above the hole (put a brick on it) hold the plasterboard in place with a couple of screws though the new plasterboard and through the existing ceiling, use polyfiller to finish.

Tungsten halogen lights burn at 39 degrees C polystyrene begins to melt at around 340 degrees C. Insulating the existing lights is do able. But, tungsten lights burn out sooner if they are allowed to get too hot.

Take a look at pollyfillers cream to cover Artex.

Note: The amount of asbestos in Artex was very small. If you merely cover it over, no problem.

Do not sand it down or off!

The rules regarding asbestos relate to people working with asbestos on a day to day basis.
There is asbestos in the air all the time, we everyone in all parts of the world, breath it in every day, it does us no harm.

There is a very large industry based on doing things that are not required but, enable some people to become very rich.

Water vapour is a very tiny gas, that can and does move through most things. It is like having a box full of footballs (the air) and in the spaces between there are from time to time a quantity of very tiny ball bearings (the water vapour).

The theory behind vents in lofts is, that rather than solve the problem of humidity at source, you spend a lot of money in creating a system that relies on the passing wind to suck the water vapour from the loft. Unfortunately, the wind does not always blow and the system does not work as intended.

The wind pulls the warm air from the home through all the cracks, holes and vents that people fit, removing the water vapour and at the same time costing a lot of money in having to heat the cold air that replaces the warm.

When the wind does not blow, on cold winter nights and days, the water vapour moves into the loft and condenses on the nearest cold surface, usually the slates and tiles. A small amount does no harm, not like in Canada where over the winter the whole loft can fill with ice with consequences when it melts in spring.

Water vapour always move from warm to cold and from areas of high pressure to areas of low pressure, warm air rises as does water vapour.
Think equator and clouds forming, rising and moving north and south as the earth spins.

Using extractor fans and or de humidifiers removes the water vapour at source, especially those with humidistat's.
Perry525
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Joined: Fri Jul 06, 2007 7:35 pm


Postby Ian Dudley » Thu Sep 30, 2010 9:52 am

Thanks for the detailed response.

I was under the impression that the new insulation rules are only for new bulid, not existing homes? I'd also read that a certain level of ventillation is mandatory, which is often delivered (but doesn't have to be) via trickle vents. So I'm surprised to hear that they are apparently banned? If you block up the house completely you're going to need an expensive ventillation system to avoid having exactly the problems I have now. Fine if you're buliding new, but pretty daunting in an existing property.

The basic problem for me is that I have an older house, with a lot of issues in it (not just the condensation, it needs some repair work doing to a chimney stack, it needs a new bathroom, decorating throughout and the electrics probably need to be checked) and a limited budget. I'm not looking for sympathy, I bought the house knowing this stuff, but it puts practical limitatons on what I can do.

I'd love to be able to really go to town with heat reclaiming venitllation and knocking the condensation on the head at source, but I simply don't have the time or budget for it. Modifying behaviour is also difficult with a busy family needing to live in the place.

I already dropped a load of money last year on getting the boiler and rads sorted as it was banging like a blacksmith and burning god knows how much gas. Needed a new HW cylinder as well. I also had to completely re-paint the outside as the old paint was falling off the walls.

Right now we get by with a de-humidifyer in the central hallway, plus leaving lots of doors open to let the air circulate. But over time I want to try and improve the situation as cheaply and efficiently as I can. Sure, putting more vents in increases my fuel bills a bit, but not by a huge amount compared to the cost of major works through the house. Right now if I can just normalise the house, i.e. get it to a position where we don't have mould growing in every dark corner every winter, I'll consider that a win.

Then in a few years time when I've got on top of the major stuff I can come back and look at this longer term in conjunction with energy efficiency. As I said I need to do the windows sometime, and the loft insulation and boarding probably could do with being completely redone, so that sounds like a good time to look at the whole issue. But that's a project for the future.
Ian Dudley
Posts: 8
Joined: Fri Dec 05, 2008 11:18 am


Postby Perry525 » Wed Oct 06, 2010 1:03 pm

That is true, I was bring them to your attention to advise future practice, which has a bearing on your problem.

Again this was true, but it does not apply to existing stock and will not apply to new build.

While the new reulations will apply to all new office blocks and factories from 2020, in practice all new builds already comply with the new standard, if they did not....they would not find any customers at top prices.

If you eliminate uncontrolled ventilation, which costs an enormouse amount of money every year in wasted heat, you can still open a window, that is controllable and costs little.

AS I wrote earlier, water vapour is self inflicted. Cold walls that create condensation, damp and heat loss are down to poor air circulation and lack of heating......and of course as I wrote earlier, they were designed and built that way.

If you go on the net and look up condensation, you will find that for every given temperature there is a dew point.
This is the point where water vapour drops out and forms condensation.

If you keep the room temperature steady, or pay attention to dew points and only turn your heating down the correct amount, condensation goes away.

You can buy indirect cylinders on e-bay at reasonable prices, you can also pick them up a council tips, where they are being dumped.
Why do you need a new cylinder? There is very little that can go wrong with them.

At the end of the day, you need a list of priorities....only you can decide how, when and where to spend your money.

We merely advise what is possible.

By the way, buy a infrared temperature gun on Amazon, this will tell you the surface temperature of everything you point it at, ideal for identifing how cold a wall is.
Perry525
Posts: 722
Joined: Fri Jul 06, 2007 7:35 pm


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