How to Convert a Loft

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Want to add space and value? Then consider a loft conversion, says Paul Hymers
Truss Loft conversion project

Before you begin on your loft conversion, it is worth finding out exactly what it will involve and how it will affect the design of your home. Here are the 10 key things you need to consider when weighing up whether a loft conversion is the right way to add more space to your property.

1. Can your home take the weight of a loft conversion?

Clearly it’ll add weight to your house and, although it may only be a modest increase, you’ll need to make sure that the structure of the building can take it. You’ll need to expose the foundations and check them, together with any beams or lintels that will be asked to carry more weight.

Your Building Control officer will also want to check all these elements, so dig a small hole to expose the foundations first. If it turns out that your house needs underpinning to support the extra weight, it could double your budget before you start.

2. Is there enough head height?

Get your designer to illustrate clearly how much headroom you’ll have in your loft once it’s converted – people are often disappointed by how much space they have to actually stand up in and on plans this isn’t always clear. Don’t forget you’ll have to accommodate a staircase leading up into the loft – to make the best use of space the new staircase should rise above the old one and not from within an existing bedroom. There’s not much point in converting the loft space if it means losing an entire room on the first floor.

Without the roof space for water tanks and plumbing, the heating and hot water system may have to be replaced with a sealed system. It’s better to have an unvented hot water cylinder than a combination boiler, but it will take up a cupboard-size room and you’ll need to find somewhere to put it.

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3. Building Regulations & Party Walls

Loft conversions always need approval under Building Regulations (irrespective of whether they need planning permission) so it pays to adopt the full plans application approach and have a detailed scheme approved before you find a builder. Having an approved design will take much of the risk out of the work and also mean the builder has a chance to give you a fixed quotation, rather than a vague estimate.

If your house is semi-detached or terraced don’t forget to notify your neighbour of your proposals, which will usually fall under the Party Wall Act 1996.

Your Building Control officer will inspect the work at various stages and on a final inspection should issue you with a completion certificate – don’t settle any final accounts with contractors until you’ve received the certificate.

4. Altering the roof structure

Most roofs are constructed with internal support struts in the loft, propping up the rafters and purlins (horizontal roof beams) in traditional cut and pitched roofs, and making up the web of braces in modern trussed rafter roofs. All these have to be removed to make way for the new room and replaced with new supports that don’t impose on the space.

There are many ways of altering roof structures for loft conversions, but they all have one common element –the ceiling joists will almost certainly be inadequate as floor joists. This means that new floor joists are fitted alongside them, slightly raised above the ceiling plasterboard to avoid contact with it.

These joists (often 200mm or 225mm in depth) will rise above the tops of the current ceiling joists to form the floor structure. Depending on their span they will bear either directly on to the existing wall plates of external and internal load-bearing walls, or on to newly installed beams.

In smaller lofts, it is often the case that the floor joists themselves will be used to support the sloping rafters. This is possible by constructing a dwarf timber stud wall 1m to 1.5m high, known as an ashlering, between the two. With the supporting ashlering in place, the internal struts and braces can now safely be removed.

5. Loft conversion stairs

Stairs are invariably tricky to design, as space for them is tight. Narrow winding flights are acceptable, but may prove impractical, because it’s difficult to get furniture up them. Purpose-built staircases are around 10 times the cost of standard (off-the-shelf) designs, so bear this in mind when you’re planning your loft conversion.

If you do need a purpose-built staircase, it pays to have the design approved by your Building Control officer before you actually commission them. Ask your joiner or builder to send Building Control a copy of the design. As part of the fire safety upgrade for your loft (see below) your stairways should lead to a hall and an external door. If you have an open-plan arrangement where the stairs rise from a room, it is likely you’ll have to alter it, fitting a new partition wall or choice of escape routes.

6. Fitting windows & gaining natural light

You don’t need to make a lot of structural alterations to accommodate rooflight or skylight windows, which makes them relatively easy to fit. Typically the rafters on either side of the rooflight are doubled-up and trimmed across the top of the opening.

A popular alternative is to fit dormer windows, which are structures in themselves, as they have walls and a roof as well as the window itself.

At the rear of many homes dormer windows can fall into the permitted development quota and so may not require planning permission. At the front of the house, however, they will require planning permission, which is why you often see rooflights or skylights instead.

Dormer windows may be essential to maximise the headroom in the loft and provide useable space, but will need to be supported at the apex point (ridge). A ridge beam is installed beneath the apex before the dormer roof joists can themselves be fixed in place and the roof weathered. It is at this stage, when the dormer windows are being constructed, that your loft conversion will be exposed to the elements, so you’ll need good temporary sheeting to protect against the weather.

7. Upgrading for fire safety

Loft conversions on bungalows have little effect on the fire safety of your home, beyond making sure that the new windows are large enough to escape out of. But in a house where two storeys become three, there are implications. The new floor will need at least 30 minutes of fire-protection, which could mean re-plastering the ceilings below it and the loft room will have to be separated by a fire door, either at the top or bottom of the new stairs. You’ll also need one escape-sized window per room – some skylight windows are made specifically with this in mind.

Door self-closing devices are no longer required in homes. They’ve proved to be a risk to children’s safety because they can trap tiny fingers. Instead existing doors on the stairway (ground and first floor) should be replaced with fire-resistant doors or upgraded. Plans submitted prior to this date fall under the previous guidance, which required self-closing devices on all the lower doors, but you should be able to apply to adopt the new approach.

As part of the electrical installation, mains-powered smoke alarms should be installed on each floor of your home and these should be interlinked so that they all sound when one is activated. Most have a re-chargeable battery as a back-up that allows the supply to be extended from a lighting circuit if need be.

8. Insulating your loft against heat loss

With standards being increased, loft conversions have become awkward to insulate. The sloping ceiling will need insulation cut and fitted between the rafters, and on top of them. As the plasterboard will have to be fixed to the rafters through the bottom layer of insulation, you will want this insulation to be as thin as possible. So, you should use some high performance insulation (typically a foam board) for all of these areas. The ashlering walls and dormers will also need insulating with similar products before they are plasterboarded.

9. Insulating against sound

The new floor also needs soundproofing, and this is easily achieved by laying a mineral fibre quilt between the joists. Use the heavier, denser sound insulation quilt and not the lighter thermal insulation material, which is of no help here. The same goes for any internal stud partitions between bedrooms or bathrooms. You should also consider insulating any party walls, both against heat loss and noise. A lining framework of timber stud will allow you to achieve both and you can cover it with sound-rated plasterboard.

10. Storage

When you convert your loft you are, of course, going to lose storage space. Make the most of what you have by using the eaves behind the ashlering – fit access hatches and have roll-out storage bins made to fit. And if you insulate down the rafter line to the eaves you’ll create a warm store for your belongings. Built-in wardrobes are also a great feature in loft bedrooms, where standard units won’t fit.

Image: Contemporary loft conversion by Trussloft, featuring Velux rooflights that offer access to a balcony

Also related to this article


Pete Baird
Posted on

Worth bearing in mind that, if you live in a conservation area with no evidence of dormer windows, you're very unlikely to be able to get permission for one. So don't plan your new habitable loft around the extra space a dormer would bring - focus on what you achieve with rooflights and look at whether the first floor ceiling might need to be lowered slightly.

Posted on

Very useful post for anybody considering a loft conversion

Posted on

Altering the roof structure is a very delicate task. You should be really careful. I really advise you to get it done by a professional.

Callum (MyHandymanServices)

Posted on

I live in a house aprox 130yr old. There are no cross braces so it's already open. The flor to be joists are aprox six" heigh 3" wide. In no builder though. Would it b a case of flooring it and insulating and plasterboarding the roof area. I have room for stairs aw well. I know a gd carpenter. any opinions would be welcome.

Posted on

A loft conversion for your house is considered to be permitted development, not requiring an application for planning permission. Work on a loft or a roof may affect bats. You need to consider protected species when planning work on this type.

Posted on

The final sentence under Building Regulations needs better wording. It presently reads as if you shouldn't settle the Building Reg's fee until you have the final certificate. It should however, read that you may want to consider withholding your contractor's final funds until they have done everything necessary to satisfy Building Control - thus when you have got your final certificate.

Posted on

Hi I am from West London, Your article is Very useful post for anybody considering a loft conversion. Thanks you

Posted on

Hi we live in a house that has been converted into 2 maisonettes. Upstairs has converted the loft without notifying us, including putting in a permanent staircase with no door as fire protection and hasn't had anyone check what he has done to ensure they meet regulations. We have to have joint buildings insurance which he arranges being the freeholder. Does this invalidate our insurance?

Bodger Bill
Posted on

Possibly the best/most in-depth article on this subject...many thanks.

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