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Converting a Loft is Harder Than You Think

Updated: Feb 25

loft conversion UK
Loft conversion, before and after (sort of...)

I’ve been running my own Architecture practice in the UK since 2009, specialising in alterations and extensions to private homes. In general, I love my job, but if there is one kind of alteration that I don't enjoy its the loft conversion. I can see the appeal for homeowners, the loft is sitting there doing nothing except storing the Christmas decorations and holiday luggage, why not convert it to a habitable room, maybe even two rooms. I have lost count of the number of clients who call me up, excited at the possibility of getting loads of extra space for not much money. The roof has already been built, how hard can it be?

It turns our loft conversions are a lot harder than you think. Lets start with height. I am taller than average, well over 6 foot, that’s 1.9m in metric. So I am sensitive to low ceilings. Most homeowners stand in the loft, under the highest point of their roof and think they have loads of headroom. What they don't consider is the width of that roof and the fact they will need adequate headroom across a wide area.

It might surprise some people to learn that the building regulations in the UK don't set a minimum height for habitable rooms in private homes. Even without a minimum height for the ceiling in the regulations, there are practical limits on what can be used as a habitable room. The Royal Institute of Chartered Surveyors set a minimum of 1.5m headroom when surveying a property for sale. Any space with less headroom than that wont count towards the square footage or meterage of the property.

Then there is insulation, this further decreases headroom. A conventional, pitched roof with rafters must be upgraded to meet the thermal requirements of the building regulations. In Scotland in 2023 that means meting a U-Value of 0.12 If you don't know what a U-value is, it measures the amount of heat that escapes per square meter per hour and 0.12 is a low number, which requires a lot of insulation.

Take a look at this online u-value calculator from Kingspan. This isn't a paid advert, I use their products regularly and they work. This shows that to achieve the 0.12 u-value we must have at least 100mm insulation between the rafters and 82.5mm insulation backed plasterboard fixed to the inside of the rafters. That lowers the ceiling by 82.5mm. Thats more than 3 inches.

roof insulation
Example of roof insulation from the Kingspan website

Then there is acoustic separation. The building regulations require a minimum amount of sound deadening between rooms in a home. This will lead to the loft floor being raised so that new, thicker timber joists can be fitted. The structural engineer may also need to increase the posit depth but the overall impact of this is to reduce the floor-to-ceiling height even further.

Then the fire regulations kick in, to make life even more interesting. Contrary to what some people think, the measurement that matters isn't the number of stories, its the height from ground to the top floor measured in meters.

Lets assume you own a nice two storey house. In the UK a typical home built in the last 50 years will have a floor to ceiling height of 2.4m, combined with the floor thickness of 300mm and the loft floor thickness of at least 250mm that gives a height from ground to the new loft floor of 5.54m

a cross section drawing showing the heights from floor-to-floor

Unfortunately this puts our new loft conversion in the next category of fire risk and the building regulations give us two choices; A protected enclosure or suppression. But What does that mean? In simple terms, a protected enclosure means that every door off the stairs must be a self closing fire rated door. This includes all existing doors leading off the existing stairs, not just the new ones.

If you don't like the sound of that you can use Suppression, which usually means sprinklers and they will need to be in every room in the building, existing and new alike. In most cases, fitting fire doors is the cheaper option.

Now lets assume you have an existing loft which is very large and the space exists to upgrade the floor and add all the necessary insulation and still have lots of space for new bedrooms. You will need a stairs and people make two basic mistakes when thinking about their new stairs;

  1. That it can be placed wherever suits the layout best.

  2. That a stairs can be a small, discrete item.

Wrong on both counts.

The building regulations have lots to stay about stairs. For starters they set a minimum headroom of 2m for all points on the new stairs and the landings. If the new stairs is located at the edge of building, under the lowest point of the roof, it can often mean that by the time you climb 2 or 3 steps up you will have less than the 2m minimum headroom. In most homes, the only viable place for the stairs is in the middle of the floor plan, under the highest part of the roof. The new stairs must also have a minimum width of 900mm between the wall and handrail.

Pro-tip. The most efficient form a stairs is usually a switch-back or dog-leg layout with winders. Contrary to poplar belief a circular spiral stairs is not an efficient layout.

dog leg stairs
notice how this stairs turns back on itself.

All this this usually means the stairs will take up a large chunk from an existing bedroom. In many cases that chunk is so large, there isn't enough space left for a bedroom. So the house is now down one bedroom but that’s ok, the new loft conversion will get two new bedrooms. So the house will have one more bedroom than when we started.

Its at this point the penny drops for most people, it isn't worth paying £40 - £60k + VAT to gain one additional bedroom. I suspect that of all the people who called me over the years asking for a loft conversion, Ive talked more than 90% out of it. Even those who went ahead were less than thrilled by the amount of space they got, relative to the stress, hassles and cost of the project.

If you are thinking of a loft conversion you can book a consultation with me to discuss what is possible

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