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The building was sealed up, and now the air is wrong
Five things people notice, crossed with the four reasons a building ends up sealed. What to measure, what it usually turns out to be, and the parts of this that are not a heating and cooling contractor’s to solve.
Three things that apply to every answer below
- Sealing a building is not a mistake. Sealing it and adding nothing is.
A tight building is easier to heat, easier to cool and very much quieter, and in a city under an approach path that last one is not a small thing. What a tight building cannot do is ventilate itself by accident, which is how almost every older house in Inglewood used to manage. If the sealing happened and nothing was added, the air has nowhere to come from, and no amount of air conditioning changes that — because a central system recirculates the air already inside and brings in none.
- Measure over days. A single reading settles nothing.
Carbon dioxide is the cheapest honest indicator of whether enough outdoor air is arriving, and it is only useful as a record. A logger left in the room for a week, through the nights and the closed-up afternoons, turns a disagreement into a graph — and it frequently shows the problem is one room and six hours long, which is a much smaller problem than the one everybody assumed.
- Nothing on this page is a health finding.
We measure carbon dioxide, humidity, airflow, extract rates and pressure, and you get every figure. What any of it means for somebody’s breathing, sleep, headaches or allergies is a medical question, and we are not qualified to answer it. Anybody in this trade who connects a reading to a symptom in order to sell a device is making a claim they cannot support.
Work out what to measure
Pick what you have noticed and pick why the building is sealed. Every answer below is on this page whether you pick anything or not — the picker only narrows it down.
This is the one case on the page where the honest answer is partly outside your control, and it is better to know that at the start. In a multi-unit building the air in your unit is decided by things you do not own: whether the corridor is pressurised and by how much, whether the shafts serving the bathrooms still move air or were capped during some past works, what your neighbours’ extract fans are doing, and where the building leaks between units rather than to the outside. We can measure inside your unit and we will — carbon dioxide, humidity, extract flow, and the pressure difference between your unit and the corridor, which is frequently the whole story. What we cannot do is fix a building from inside one apartment. We also will not work on common parts, shafts or corridor systems on one resident’s instruction; that needs the owner or the association, and we will tell you so rather than start and stop. The measurements are worth having anyway: they are what turns “the air is bad” into something a manager has to answer.
Leave a carbon dioxide logger in the room for a week before anybody proposes equipment.
Stuffiness is the symptom most often treated by guesswork and most easily settled by measurement. Put the logger where people actually are, at the height they are, and leave it through the nights and the closed-up afternoons. The shape of the graph tells you whether this is a ventilation problem at all, and if it is, which hours it happens in.
What stuffiness usually turns out to be
In the great majority of houses we measure, it is one of four things, and three of them are cheap:
- An extract fan that is not connected to anything, or is connected to a duct lying beside its terminal in the attic. It runs, it makes a noise, and it moves almost nothing.
- A bedroom with the door shut and no return path, so the room is starved of air movement for eight hours a night. This is why stuffiness is so often a bedroom complaint and so rarely a living-room one.
- A recirculating kitchen hood, which filters grease and returns everything else, including the moisture, to the room.
- Nothing bringing outdoor air in at all, which is the real answer in a genuinely sealed house, and the only one that costs money.
We work through them in that order, because the first three are hours of work and the fourth is a project. Measuring again after each one is the only way to know which mattered.
Find out whether the moisture is being made inside or getting in. They have opposite fixes.
Moisture generated indoors — showers, cooking, drying laundry, breathing — is a ventilation problem, and the answer is getting it out. Moisture arriving from outside or from below is a building problem, and ventilating harder can make it worse by pulling more in. A week of humidity logging in the affected room, compared with outdoors, separates the two, and it has to happen before anybody spends anything.
Damp in a sealed house, in order of likelihood
Start with what the building is doing. A house on a raised foundation with a damp crawl space will push moisture upward all year, and a sealed house gives it nowhere else to go. Ducts running through that crawl space, leaking on the return side, will draw it directly into the air you breathe — which is both a damp problem and a reason to measure duct leakage rather than estimate it.
Then the obvious generators: a bathroom fan that does not extract, laundry dried indoors, and an unvented gas appliance, which produces a great deal of water vapour as well as everything else and should not be in use in a sealed room.
Then the equipment itself. A cooling system that is too large satisfies the thermostat quickly, shuts off, and never runs long enough to condense moisture out of the air — the house ends up cool and clammy, and adding capacity makes it worse. In a mild coastal climate this is a genuinely common finding and it is the opposite of what people expect.
Where there is visible mould, we stop and say so. We will find and fix the moisture source, because that is mechanical. Testing for mould, identifying it and removing it belong to an industrial hygienist and a remediation contractor, and a firm that offers to test and then sell you the cure has an obvious conflict.
Find the path before you look for the source. In a sealed building, smells travel by pressure.
A smell that appears in one room and not another is following a pressure difference, and pressure differences are measurable. Before anybody starts guessing about neighbours, garages or drains, we measure which way the air is moving between the affected room, the rest of the building and outside. The path usually names the source without anybody having to accuse anything.
How a smell gets into a room that seems closed
- The return side of the duct system is leaking into a crawl space, an attic or a wall cavity and drawing whatever is there into the house. This is the commonest cause and the least suspected.
- An attached garage is being depressurised by an extract fan or by the duct system, and air is moving from the garage into the house rather than the other way round.
- A dry trap on a floor drain or an unused bathroom, which is a plumbing matter and a five-minute check.
- A shared wall or a shared shaft in a duplex or an apartment, where the path is between dwellings. This is where we measure, write it down and go no further — see the note about buildings you do not own.
Charcoal filters and plug-in devices remove the complaint from the room without removing the path, which is why the smell always comes back. The measurement is cheaper than several years of that.
Check whether anything on the property brings in outdoor air at all. Frequently nothing does.
The sensation of air that is moving but not fresh is almost always exactly what it sounds like: a recirculating system doing its job. The question is not whether the air conditioning is working — it probably is — but whether any outdoor air is being introduced anywhere, and in most houses the honest answer is none.
What bringing air in actually involves
There are three honest options and they differ mainly in cost and in what they do with the energy.
- Exhaust-only. A quiet continuous extract, usually in a bathroom, running at a low rate. The replacement air comes in through whatever leaks remain. Cheapest by a distance, and it works less well the tighter the building is — which is exactly when you need it.
- Supply ventilation. A filtered outdoor air path brought into the return side of the system with a control that runs it on a schedule. Modest cost, the incoming air is filtered and tempered, and the house is kept slightly pressurised, which also helps with the smell problem above.
- Heat or energy recovery. Two air streams, balanced, that never mix, with a core that recovers most of the temperature and in some units some of the moisture. The most expensive and the most controlled, and in this climate it is a comfort and consistency decision more than an energy one. We will tell you when the numbers do not justify it.
All three are sized against a rate, and the rate comes from the house. We will not fit any of them before the cheap findings have been dealt with and measured again, because it is entirely possible to spend a lot of money ventilating a house whose extract fans were simply disconnected.
Do not open the window. Getting the air in mechanically is the whole job, and it is solvable.
If the only way to make a room breathable is to undo the thing that makes it liveable, the building is asking for mechanical ventilation and has been for years. This is the most satisfying version of the problem to fix, because the answer is unambiguous and the result is immediate.
Air without the window, in a building under a flight path
The equipment is the straightforward part: a filtered supply path or a recovery ventilator, sized to the rate the rooms need. The part that takes care is making sure the ventilation does not become the new noise. That means generous duct sizing so the air is not forced, fittings that do not make it turn sharply, lined duct where it passes anything sensitive, a unit sited away from bedrooms and isolated from the structure, and terminals chosen for the volume rather than for how they look.
It also means thinking about the path itself. A duct through an external wall is a hole in the thing that was keeping the noise out, and a straight short duct with a plain grille will let a surprising amount back in. Lined, bent and correctly terminated, it will not.
What we will not do is replace your windows, advise you about acoustic glazing, or certify anything about sound. We measure sound pressure before and after so you can hear the difference and also see it. Rooms signed off to a criterion belong to an acoustic consultant.
If the windows were replaced for aircraft noise
Then the sealing was done deliberately and well, and it worked — which is precisely why the ventilation question arrives afterwards. A window that no longer opens, or that nobody wants to open, is a ventilation opening the house has lost, and older houses here were designed around having several.
Worth establishing early: whether anything was added at the time. Sound insulation work sometimes includes mechanical ventilation and sometimes does not, and whether it did is a matter of what was actually installed rather than what people remember. We will find out by looking, which takes minutes.
We have nothing to do with the airport’s sound insulation programme. It is run by the airport authority, with its own boundaries, rules and timetable, and it is not ours to interpret. We cannot tell you whether you qualify, what it covers, or whether it is still open. Ask them directly, and treat anybody who implies they can answer for them with caution. What we can do is the mechanical work, whether or not any programme is involved.
If it was a weatherisation or air-sealing job
Then somebody has reduced the building’s leakage on purpose, and the first question is whether ventilation was specified alongside it. Good air-sealing work includes it. A great deal of work does not, particularly where the sealing was done piecemeal over years — new windows one year, attic insulation and can-light sealing another, a door and some caulking after that. Nobody ever decided to seal the house; it simply happened.
The tell is usually seasonal. A house that was fine and became stuffy, or where condensation started appearing on the inside of windows that never used to show it, has crossed a threshold. That is not a fault in any of the work — it is the predictable result of doing half of a two-part job.
The good news is that the expensive half was the sealing, and it is already done. Adding a controlled, filtered, measured supply of outdoor air to a tight house is cheaper and more effective than trying to ventilate a leaky one, because you are choosing where the air comes from instead of hoping.
If it is an apartment or a unit in a shared building
Then read the note above first, because it is the important part. Inside your own unit there is still real work to be done and it is worth doing: the extract fans measured and made to work, the return path between rooms sorted out, the duct leakage established, and a week of logging so that what you are describing has a shape.
Two findings come up again and again in small buildings here. The first is a bathroom or kitchen shaft that was capped or restricted during past works and now moves a fraction of what it should. The second is an extract that is pulling air from the corridor rather than from outside, which means the corridor’s air — and everything in it — is what you are ventilating with.
Both are findings a managing agent or an association has to act on, and neither is arguable once it is a measurement with a date on it. That document is frequently worth more than anything we could install.
If it never had any ventilation at all
Which is true of most houses in this city built before the codes required it, and is not a defect so much as a historical fact. These houses ventilated through their windows and their leaks, and they did it well enough that nobody thought about it.
What changes the picture is anything that reduces the leakage or stops the windows being used — and in Inglewood that is nearly everything: replacement windows, air conditioning that makes closed windows normal, security concerns that make open windows unattractive at night, and the noise.
The order we would suggest is the cheap one. Get every extract fan in the building actually working and measured. Make sure air can get back out of bedrooms with the doors shut. Vent the kitchen hood outside if it recirculates. Then log for a week and look again. A surprising number of houses need nothing further, and the ones that do will have a number attached to how much.
Where this page stops
We will measure carbon dioxide, humidity, extract flow, airflow, duct leakage and pressure differences, log them over days, and give you every figure with the date and the method. We will fix what is mechanical and we will tell you plainly when the cheap answer is the right one.
We will not attach a health outcome to any reading, sell an air cleaner on a symptom, test or remediate mould, replace or advise on windows, certify sound or ventilation compliance, speak for the airport’s sound programme, or work on a shared building’s common parts on one resident’s instruction. If a reading ever indicates carbon monoxide, that is the one item on this page that is urgent and it is dealt with immediately. Everything else here can wait for a week of data.