Nine years ago, the collapse of a section of the ceiling at the Apollo Theatre in London left theatre-goers covered in debris with about 76 injuries.  This brought into focus the need to maintain ceilings in period properties.

Looking at the pictures of the Apollo’s interior there is much ornate plasterwork but being built in 1901 the base of the ceiling will undoubtedly be of lath and plaster type. The laths (approx. 32mm wide by 6mm thick) are securely nailed to the timber joists above but the lime based plaster, which can be up to an inch thick, is held in place by being forced through the gaps and hooking over the tops of the laths where it sets.

The ceilings of modern properties tend to be plasterboarded and skimmed and are considerably more stable.

Lath and plaster ceilings do not react well to vibration or water ingress. Plaster is brittle by nature and will crack at its weakest point under vibration. In practice that means the nibs that wrap around the laths and keep the ceiling in place snap off. If enough of them snap off the weight cannot be supported and the ceiling collapses.

Similarly, water from above soaks into the porous plaster and weakens the nibs. Some onlookers at the Apollo Theatre were quoted as saying water dripped through the ceiling just before the collapse on what was a very wet evening in London. It is unlikely that water ingress on the evening would have been enough to bring the ceiling down but if water had been dripping undetected over a long period on to a ceiling that had already been weakened by vibration the combination could have caused the collapse.

A similar situation occurred last year at a clients, a development that only recently completed.  From our experience, ceiling collapses are relatively common in older residential properties that typically have lime based lath and plaster ceilings in all rooms. From our clients narration, the installation of Virgin Media broadband within the area may have led to this.  This was because, the property upstairs was empty and Virgin Media a few days prior was operating a large digger at the front of the property and had also in the process accidentally cut off the client’s cable.

Fortunately there was nobody in the room when the ceiling came down as being hit on the head by a inch thick slab of plaster could have caused some terrible injury.  This kind of claim can seem a little far-fetched and dismissed as just a coincidence as in this case however it is the only logical conclusion.  This is why when we assess properties for our clients we look for evidence that old ceilings may be becoming unstable; unevenness, hairline cracks and hollowness are all tell tale signs. If you are worried about your own property a gentle tap with the handle of a broom should tell you whether the ceiling plaster is hollow and should be replaced.  The damages from such an oversight could be costly, particularly in a rental property.  As such when we renovate old properties we advise clients to pin plasterboards below such ceilings so as to prevent such an incident.

Of all the types of property extension the conversion of a loft space is one of the more affordable in comparison to side and/or rear extensions and they do of course, see you gain additional bedroom(s). So, what are the various types, are what do they typically cost?

SIMPLE DORMER EXTENSION

This is the most common and most affordable extension and is a good option for most property types and creates additional headroom by creating a box shape out of the rear slope of the loft, with the outside walls often set back from the party parapet wall. The roof tends to be felt, whilst the walls are finished with hung tiles.

You can typically avoid planning permission and go for permitted development instead.  Whilst not the most aesthetically pleasing of designs, it gets you an additional bedroom and possibly an en-suite bathroom. Work takes 3-4 months.

L-SHAPED DORMER EXTENSION

This is the same as above but includes an extension over the rear outrigger (the rear part of the L in a Victorian property) in which you can get either an additional bedroom, or a much larger bathroom compared to the smaller en-suite found in the simple dormer.

You gain around double the space for slightly less than double the cost, so the build can be completed in around 3-4 months.

MANSARD LOFT EXTENSION

This design is more aesthetically pleasing as it involves the raising of the party parapet walls in brick which creates slightly more space and increased head height versus a dormer and is often seen in properties with butterfly roofs where such raising is essential.

Planning permission is almost certainly going to be necessary, with costs and time rising slightly compared with a dormer on sloping roof properties. This type of work takes about 4-5 months.

HIP TO GABLE CONVERSION

This type is found in end of terraced, semi-detached and detached properties or bungalows and involves extending the inwardly sloping roof, creating a vertical wall. They are more expensive than mid-terraced dormer extensions by virtue of having to build up the side of the roof to then create a dormer. Semi-detached properties can end up looking lop-sided if only one neighbour has undertaken a conversion.  The conversion takes about 4-5 months.

What Next?

A good architect will show you how to maximise the space you have for your budget and advise you which options do and don’t require planning permission. They will produce planning/conceptual drawings and then drawings that are suitable for Building Regulation approval and you will also need an engineer who will determine where the steel beams are located having undertaken loading calculations.

Unless you are in a detached house, you will need to consider the Party Wall Act, ideally 2-3 months before you plan to start works.  Loft conversions in the grand scheme of things are relatively straight forward, but it is still worth giving your neighbours the heads up to maximise your chances of a favourable response.

If you own a flat, then it is most likely that you do not own the loft space and it will need valuing, and a premium paid of between 5 to 10% of the property value to your freeholder in addition to build costs and professional fees. Your freeholder is may insist on a license to alter, which protects their interest and other surrounding flats.