Insufficient airbricks at rear - options?

[drpepe]

Hi I'm new to this great forum and hoped you could lend you expertise and experience to advise on my problem.

We have a 1901 terrace with a damp issue in the walls (according to homebuyer report and independent surveyor) and within the subfloor.

It has a suspended wooden floor apart from the kitchen which is solid and looks original (large 'red' flags/tiles). The soil under the suspended wooden floor is fairly close to the joists (maximum 20cm, touching the joists in some areas) and is damp clay and rubble (no standing water). Where the soil touches joists and wall plates, they are rotten. There is a smell of damp especially in the front hallway - especially noticeable when the house has been closed up empty, and a big problem with slugs.....


There are 3 airbricks in the front wall of the lounge. Whoever built the conservatory in 2001 didn't think to allow for airflow...there is only 1 airbrick at the rear (in the only place available next to the conservatory).

The internal walls have no ventilation through them (apart from under the doorways) and the pier walls run front to back. There is no ventilation in the front of the hall (the worst smell is here).


Our solution:
Install airbrick under the front doorstep and dig out the subfloor in the hall (where soil touches the joists).
Knock out some bricks from each of the internal walls (1 brick in each corner and one in the middle).
Install a larger airbrick in place of the small one at the rear

The limiting factor seems to be the rear where there will be only one airbrick in a very sheltered spot between fence and conservatory. Therefore my planned solution was to break up the hearth in the rear dining room (we've removed the repro fireplace) install a vent in the floor at the back of the hearth and a conduit through down into the subfloor. I was hoping the draw of the chimney would help ventilate.

I'd appreciate any comments on the issues and how we plan to sort them out.

 

[88v8]

Welcome to the forum.

Your problems are alas familiar. As someone remarked recently, the Victorians weren't very good at underfloor ventilation.

When our conservatory was built across the back of our previous house I had four or more airbricks piped under the concrete floor.
Elsewhere in the house I also put in extra bricks in various places, especially near corners where the airflow had a 'dead zone'.

The soil under the floor should ideally be covered in a weak concrete mix when the house is built. Once built, it becomes impracticable of achievement, and as an offset more airflow is desirable. Also, if you dampproof under the floor, it brings into question where the damp will try to go... is there dpc in the pier walls, the outer walls... if not the damp will go there instead.

Eight inches below the floor is a pretty minimal gap, but be aware when you dig that pier walls may have little or no footings.

I'm surprised that the soil under your house is so actively damp. Slugs....? Away from the outer walls I would not expect this.

Anyway, it is what it is. I would progress as you have indicated. One cannot have too many air bricks. The terracotta are pretty useless, the air gaps are too small. Cast iron better although you should paint them before fitting or they will rust. If you are particular about design, there were some lovely new iron airbricks on here a month or three ago (no I can't remember quite...)

Pull from the chimney... yes, excellent notion.

You've take quite a job. In a year or two you'll start to see the benefits.
Be aware that if the floors are dampish, the boards will shrink muchly as they dry. Don't be thinking of sanding and sealing 'cos you'll have whistling gaps.
Onwards.

Ivor

 

[Flyfisher]

Welcome to the forum.

I basically agree with Ivor's comments. We also had ventilation piped under a kitchen extension solid floor into the space below the suspended floor of the original house, though sadly such things are all too easily overlooked. But it seems like you have a good understanding of the issues and are on the right track to improving things.

It sounds like a good idea to increase the size of the single air brick at the rear and adding addition ventilation can only be a good thing. My understanding is that air bricks on multiple sides of a building aid the ventilation as any wind creates a slight difference in air pressures around the house that facilitates a flow of air rather than just passive ventilation.

Ventilation via the chimney is probably good for both the underfloor and the chimney itself, though I'm not sure how much this will be affected whether you install and open fire or a stove. Either way, it sounds like it should be an improvement.

Given the close proximity of your soil under the floor joists, it might be good to lower this a little if possible. Nothing too drastic that might affect the support of the floor (assuming the joists are supported on the ground in places) but enough to increase the air volume and (hopefully) reduce the underfloor humidity by dilution with more air, and certainly by enough to ensure that no subsoil is touching the joists, for the reasons you have already observed.

It might also be worth buying a max/min thermometer with a relative humidity display. These can be found online for around £10 and can be very helpful for keeping track of what's going on. I have a few dotted around the house ( attics, cellar, unused rooms etc) and it has been reassuring to see a gradual improvement over the years as I've fixed leaky roofs and improved ventilation. Expect the results to be gradual though. Your house with have stabilised itself over many years and it may take many months or perhaps a few years to reach a new equilibrium after changing things, so being able to measure things and see a gradual improvement can be a bit of a confidence booster.

In short, do the right things and be patient. Do let us know how you get on.

 

[MatthewC]

Hi.

In addition to the ideas above, I would consider adding vents in the floors to improve the ventilation. You can buy small brass grilles for this which can be screwed to the floor.

The only suspended floor here is the lounge which only had a single underfloor vent in the front wall; when I had my open fire fitted, the installers wanted to fit an above floor vent in the front wall (GII listed, in conservation area!) and only when I disagreed did they suggest a floor vent. Even then, they were going to put it near the front wall, but I asked them to put it furthest from the front beside the chimney breast. It gets a good draught and is now helping the entire floor to be much better ventilated.

Matthew

 

[plasticpigeon]

My house seems very much like yours a circa 1900 terrace. My only air vents are 2 under the bay window and one at the back. The kitchen floor is solid and so is the front vestibule or whatever its called so no air bricks there. The sleeper walls are solid but there is obviously an air gap under the boards the size if the joists (3"). There is a big hole in the hall wall below floor level just after the solid vestibule floor to allow air to flow under the stairs, and another big hole under floor level to allow air to flow from under the stairs to the main area under the suspended floor. Amazingly the only rot we had was close to the solid kitchen floor, and I believe that was because the quarry tiles were covered with 3 layers of vinyl making that floor under damp, and the air bricks at the front were pretty much blocked by gorse bushes. We don't have damp now, although I would say the ground is around 12" below floor height in the crawl (if you're small) space. This lengthy description is to show that with even minimal air flow it is possible to have a dry subfloor space, or at least in our house is is.

 

[Zebra]

Where the soil touches joists and wall plates, they are rotten.

I take it you'll have to replace them, then? Which means lifting substantial portions of the floor anyway. I would think it would be a very good idea to remove soil where it touches joists, as that can't be good - being careful not to undermine the footings of your piers, of course.

 

[drpepe]

Thanks for the replies everyone. Yes, I've come to realise that this will be a big big job - it is a shame that the previous owner(s) concentrated on trying to tart the place up, but ignored the basics...

snip//
I'm surprised that the soil under your house is so actively damp. Slugs....? Away from the outer walls I would not expect this.

I think there are several issues at play:
1) The house used to be a semi-detached, then in 20s/30s(?) another house was built attached to ours (the old side-aspect windows/doors are now interesting alcoves in our hall and kitchen). The 'new' neighbours are at a level about 20-30cm higher than us.

2) Where the party wall and the front boundary wall join (i.e. next to our front door), we have the worst damp problems internally.

3) It was here we see most slugs and damp soil was right up to the floor boards.

4) To make matters worse it is a complicated/cramped area. The soil pipe was rerouted to exit under the floor here when the bathroom was moved to the rear. There is a gully drain just outside for the rain gutter waste, and also the rest of the services enter.

5) In addition the newish block paving drive is far too high and was built up to the house and therefore covering airbricks (and has been for the last 3 years). The first thing i did was remove the 1st row of bricks next to the house, dug down a bit and filled with chippings - i think i will build a proper paved trench in the future - plenty of houses in our street already have this.

We have dug out a lot of soil, and plan to do more when we get a new floor installed. We hope to get new tongue and groove wooden floor as soon as we know the airbricks and the soil removal to date are fixing the problem.


Not a great picture but you can just see the house junction with the decrepit boundary wall which we are having repaired in a couple of weeks - does anyone know how to damp proof the junction between garden wall and house walls? A poor picture but the best i have currently. The tap is disconnected internally. The 2 flowerpots were used by the previous occupants as covers for the superfluous openings in the gully drain. The rainwater pipe is resting on that big lump of concrete, behind which there is a piece of slate (for damp proofing?). It is tempting to get this all dug up and replaced as we have no inspection chamber, rodding eye etc.

This big discoloured patch next to the door is a little disconcerting - it doesn't seem to be attached to wall or ground level, and there is no obvious damp signs in the internal wall behind (although as I previously stated, directly below is where we have the damp problem / smell / slugs). THe picture was taken during rain.

Anyway, it is what it is. I would progress as you have indicated. One cannot have too many air bricks. The terracotta are pretty useless, the air gaps are too small. Cast iron better although you should paint them before fitting or they will rust. If you are particular about design, there were some lovely new iron airbricks on here a month or three ago (no I can't remember quite...)

I think cast iron is beyond our budget right now - we were thinking of terracotta under the door step - do you think these would be better than terracotta?

Pull from the chimney... yes, excellent notion.

I am hoping to implement this asap. I begun breaking up and removing the hearth this weekend. Does anyone have any advice on the products I could for ventilation the ventilation grille at ground level?

Sorry for the long post, but any advice really appreciated as we feel we are largely operating from guesswork!

 

[drpepe]

Just remembered another point.

I have a builder coming to reset/repoint the stone garden wall that abuts the house.

How would he go about damp-proofing the house from the boundary wall as no doubt some of the issue is water penetration via this route...?

 

[Roger440]

And even the air bricks you have may not actually be clear!

I recently had the privilige of goung under the lounge floor to investgate a sewage smell (turned out to be next door). I took up the floor in the corner right next to the air brick. Which basically, in the cavity was blocked with bits of brick and bits of mortar. Whilst there was visible daylight, by the time i finished, it was multiple times better.

Fortunately it was completely dry anyway, but worth considering checking if you are having issues.

 

[88v8]

Cast iron not that dear unless you buy the really fancy.
http://www.ebay.co.uk/itm/cast-iron-air-brick-traditional-9-x-3-225-mm-x-75mm-heavy-duty-/181502186287?pt=LH_DefaultDomain_3&hash=item2a425f932f
This and other hits from search..... Cast iron air brick.
Plastic? Yuk, sorry.

Wouldn't rush to put in new floorboards, it will take a year or two to dry out the house, but only a month or two to swell up your new boards, and tg is a pain in the proverbial when you want to take it up again, which you will.

Some plastic dpc between garden wall and house, you can get it 12" wide, perhaps more.

Brass grille fireplace
http://www.ebay.co.uk/itm/A-Superb-Bronze-Brass-Marine-Heating-Air-Conditioning-Vent-Grille-/251633060084?pt=UK_Antiques_DecorativeAntiques_Collectables_EH&hash=item3a967fc8f4
Big.......

Search string Brass grille.

Once you have sorted the ventilation - I second the comment about the existing vents perhaps being blocked, in my previous house the joists were only an inch away from the wall and I had to cut and relocate them - there will be a hell of a gale through that vent, you might prefer something closeable
http://www.ebay.co.uk/itm/Chrome-or-Brass-sliding-Hit-Miss-oblong-ventilation-vent-grill-6-x-3-/141389569043?pt=UK_Antiques_Architecural_RL&hash=item20eb799c13

Antique closeable grilles hard to find. Although not impossible.
http://www.ebay.co.uk/itm/antique-solid-brass-ventilation-grill-/111448228429?pt=UK_Antiques_Architecural_RL&hash=item19f2d5024d

Pricey, you may say, but you'll only do it once. The quality remains when the price is forgotten.

Yes, that patch next to the door is odd. Is it damper, as it appears, or dryer?

High external ground level and no dpc is a hard combo to beat... the house may never be really dry... ventilation is your friend.
Meanwhile, this will enable you to measure your progress
http://www.amazon.co.uk/Digital-Hygrometer-Thermometer-Humidity-Temperature-White/dp/B00HIDKKQG/ref=sr_1_3?ie=UTF8&qid=1409647638&sr=8-3&keywords=humidity+gauges

Scatter a few around the house.

Inside, avoid adding to the problem. Tumble dryers, showers, drying washing indoors, kitchen with no extractor, etc. Damp is damp wherever originating.
Watch for mould behind furniture against walls, and on books.

You're right to give all this priority.

Ivor

 

[drpepe]

Thanks again for the comments.

I think you're right that the vents may be blocked somewhat internally - the one at the rear was blocked with cement or render!! It looked like whoever had been doing the plastering (suspect the dodgy conservatory people) had just dumped the spare under the floor, which happened to be where the only air brick is... I have cleared that now and will do the front ones soon.

I have been investigating the fireplace/hearth area in the dining room. As with most of the house, there has been a bodge when the concrete for the hearth was poured (not original by the looks of it) so that joists are in contact with rubble and soil. All very damp. I've started digging out in this region and noticed that the fireplace looks to have been altered, making the opening smaller.

Is my interpretation correct and can the 'new' brickwork on either side and the lintel be removed? Presumably there is an arch somewhere above the metal lintel? The lintel only extends a couple of cm into the 'new' brickwork so must be contemporary with that?

I'd like to open it up if possible and use for storage (and ventilation as described in the previous posts).

 

[Flyfisher]

It's certainly not uncommon for fireplaces to be made smaller (I discovered three previous fireplaces when I opened up our inglenook) but I'd be wary of making any assumptions about a higher arch or other support and would want to see it for myself.

I'd be removing the plaster above the exposed opening in the hope of finding an arch or another lintel.

 

[stuart45]

When a chimney breast is built the jambs are built first in 9 or 13 inch brickwork and a concrete lintel over and then the rest is built up forming the builders opening.
The fireback is put in later with the brickwork at the side of it used to fill in the gap and a throat lintel over it. Yours looks like the brickwork was used as a fireback. Normally the infill can be removed leaving the builders opening.

 

[plasticpigeon]

I am going to have to reinstall the infill in my fireplace in order to install a fireplace insert. A lot of people remove all the infill to reveal the larger builders opening but I don't think that looks very good. What are you planning to put there??

 

[drpepe]

When a chimney breast is built the jambs are built first in 9 or 13 inch brickwork and a concrete lintel over and then the rest is built up forming the builders opening.
The fireback is put in later with the brickwork at the side of it used to fill in the gap and a throat lintel over it. Yours looks like the brickwork was used as a fireback. Normally the infill can be removed leaving the builders opening.

Thanks for the reply!

I'm knocking off the plaster in any case as there is evidence of damp (the wallpaper came off very easily and the underlying gypsum plaster is stained dark on both jambs).

From what you describe it sounds like I could (potentially) remove the 'inner' brick work on both sides?

 

[drpepe]

Hi everyone, a little update and query...

I have dug out a load of loose soil and rubble from the dining room - it seems to be very evenly spread (about 2 bricks height), so I assumed that that was the original ground level under the floor.

However once all that crap is removed there appears to be a layer underneath. It is pale in colour and quite hard/crunchy, with black flecks in it (see pic below).

My question - is this the original oversite or is it natural? I am quite heartened as this may mean that cleaning the entire underfloor to this level may really help eradicate the damp soil smell, the slugs and possibly the 'rising' damp detected in the walls. What it also may mean is that the idiots that built the conservatory decided to dump the mud from the footings into the floorspace, rather than remove it through the house...

 

[plasticpigeon]

Yes probably the original oversite concrete, and conservatory cowboys dumping soil under the house to save on skip costs sounds very plausible, likely even.

 

[drpepe]

Yes probably the original oversite concrete, and conservatory cowboys dumping soil under the house to save on skip costs sounds very plausible, likely even.

yes these are the same builders who didn't put any ventilation through the concrete floor they made for the conserv ... and then blocked the remaining single airbrick with rubble and soil. :evil:

 

[Zebra]

I had those builders here. They dumped a load of rubble into the void beside the chimney, then bricked it in. Hard work carting all that out again drpepe, but looking very hopeful for an improvement!

 

[drpepe]

I had those builders here. They dumped a load of rubble into the void beside the chimney, then bricked it in. Hard work carting all that out again drpepe, but looking very hopeful for an improvement!

Thanks - Yes, we have made many many trips to the tip with buckets of soil...

We have a very sick, maltreated house :roll: mainly due to lazy previous owners I reckon... slowly we're sorting it.

This year it's the subfloor and ventilation.

ONce we can be happy that problem is sorted we'll start the fun stuff like replastering, new wood floor, kitchen and some reorganisation to fit a downstairs toilet in... (not necessarily in that order!)