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Section 3 of Approved Document F Volume 1 sets out how work on an existing dwelling in England should treat ventilation. Where building work affects it - the examples given include replacing a window or door and doing energy efficiency work - the ventilation should either meet the standards in the relevant approved document or be no less satisfactory than before the work was carried out. The document is explicit that ventilation through infiltration counts as part of a dwelling's ventilation provision, and that reducing infiltration might push indoor air quality below the standard.

It then gives a simple method for judging that. Table 3.1 lists energy efficiency measures and labels each as minor or major: sealing around structural or service penetrations is minor, as is replacing a loft hatch with a sealed and insulated unit, while sealing or insulating a suspended ground floor is major, as is removing or sealing over a chimney. Measures already fitted since the dwelling was built are counted alongside the ones planned, because the concern is accumulation. Diagram 3.1 then places the total into Category A, B or C. Category A means it is likely no further ventilation is needed; Category B means further provision should be made, by natural ventilation, continuous mechanical extract or mechanical ventilation with heat recovery; Category C means the reduction is significant and the natural ventilation option requires expert advice on sizing and positioning.

Two caveats matter for a homeowner. First, a note to Table 3.1 says draught-proofing measures might not on their own constitute building work, though they may be controllable under the Building Regulations if carried out as part of other building work - so a stand-alone door seal is not usually a building control matter, while draught-proofing bundled into a wider retrofit can be. Second, this is English guidance: Scotland works to its own building standards technical handbooks, Wales publishes its own approved documents, and Northern Ireland has its own regulations and technical booklets, so check the position where you live.

There is one part of draught-proofing where enthusiasm is genuinely dangerous. An open-flued appliance - an older gas fire, a back boiler, a solid fuel stove or an open fire - takes the air it needs for combustion from the room, and that air arrives through the ventilation the installer allowed for. Blocking an air brick, sealing a floor vent or covering a purpose-provided ventilator in a room with such an appliance can starve it, which is how incomplete combustion and carbon monoxide happen. If there is any combustion appliance in the room, the permanent ventilation serving it is not a draught to be eliminated.

Trickle vents in window frames are the same argument in miniature. They are there as background ventilation, and taping them shut in January is a reliable way to produce streaming condensation on the glass and mould in the reveals by February. If the room is draughty, the fix is to seal the uncontrolled gaps and keep the controllable vents, not the reverse.

Sub-floor air bricks serving a suspended timber floor are a third case. They ventilate the void beneath the boards and keep the joists dry; blocking them to stop a draught underfoot invites rot and, in older houses, conditions that suit wood-boring insects. The right answer for a cold suspended floor is insulation between the joists and sealing at the board level, with the void ventilation left alone.

Autumn is the obvious season and it is also the practical one, because a cold, windy day makes the leaks findable. A survey done in July with the windows open tells you almost nothing; the same walk round in October with the heating on and a stick of incense tells you where the money is going.

Timber moves through the year, and that changes the job. A hardwood or softwood external door that seals beautifully in a dry August will swell in a wet November and bind, which is why fitting a compression seal to a tight summer gap is a mistake. Sash windows are the extreme case: the sashes are made to run with clearance, and the correct repair is brush seals in routed grooves rather than filling the gap with a stiff strip.

Spring is when the consequences show up. A house that was aggressively sealed over winter and had no extract running will have condensation marks in the corners of cold rooms, black spotting in window reveals and a musty cupboard or two. That is the signal that ventilation has been reduced below what the dwelling needs, and it is a reason to add controllable ventilation rather than to undo the draught-proofing.

This work is quoted by the opening and by the awkwardness of each one. A modern uPVC door needing a new gasket is quick; a Victorian panelled front door that has dropped, a bay of sash windows needing routed brush seals, or a suspended floor that has to be lifted and insulated are jobs of a completely different order. The other things that move a quotation are the number of chimneys and whether any are still in use, whether a loft hatch is being replaced rather than sealed, how many service penetrations need closing, and whether additional ventilation has to be introduced because the measures add up to more than a light touch.

LokalMatch is the front door to those quotes rather than the tradesperson. Describe the property, the openings and the draughts you actually notice, add your postcode, and businesses that do this work in your area contact you themselves. Homeowners use it free of charge; the pros pay for the enquiries they receive. LokalMatch does not carry out draught-proofing, does not set prices and does not vet, rank or recommend the businesses that respond, so the checks on competence and on anything involving a combustion appliance remain yours.