The 1930s Semi In Worsley And Boothstown

Key takeaways

• Hipped roofs have more edges and junctions than a plain gable roof, and edges are where roofs fail.
• The bay roof is the most neglected surface on the house and a very common source of damp.
• Original clay or concrete tile from this period is at or near the end of its expected service life.
• These roofs were built before ventilation was designed in, which matters once a loft is insulated.
• Semis share a party wall and often a stack, so a neighbour's condition is relevant to yours.

The shape of the thing

The classic semi of this period has a main roof running front to back, a hipped end on the outer side where the roof slopes in three directions rather than two, a projecting bay at the front with its own small roof, and a chimney stack on or near the party wall. Some have a gable rather than a hip. That geometry is the key to the whole building, because every place two surfaces meet is a junction that depends on lead or mortar rather than on the covering itself. A hipped roof has more of those junctions per square metre than the plain gable roofs of the terraces built a generation earlier.

The hip, and why it matters

Where two slopes meet at an external angle you get a hip, and the tiles along it are covered by hip tiles bedded in mortar, sometimes with a metal hip iron at the bottom to stop them sliding. That mortar has the same service life as ridge mortar, which is to say it is now well past it on a house of this age. Failed hip mortar produces the same two problems as a failed ridge: water getting in at the junction, and heavy tiles sitting loose at height with a clear path to the ground. On a hipped roof there is considerably more of this bedding than on a gable roof, so there is more of it to fail.

The bay roof nobody looks at

The projecting bay at the front carries a small roof of its own, usually flat or very shallow, and on many of these houses it has never been touched since the day it was built. It may be lead, felt or a later replacement in something modern. It has an abutment where it meets the main wall, an outer edge, and often no gutter at all. Because nobody can see it from the ground and it is out of sight from inside, it is the single most neglected surface on the building. It is also directly above the front room, which is why damp above a bay window is such a common complaint in houses of this type.

What the covering is, and how old it is

Roofs from this period were commonly covered in clay tiles or early concrete tiles, laid on battens with no underlay or with a bitumen felt that has since become brittle. Clay from this era can be excellent and can also be variable, with poorer batches showing frost damage as flaking faces and crumbling edges. Concrete tiles of the period lose their surface finish over time and become porous and rough, which holds moss and increases weight. Either way, a covering laid in the interwar years is at or beyond the age at which it should be assessed properly rather than assumed to be fine because it has not leaked yet.

The ventilation problem these houses developed later

When these roofs were built, lofts were draughty and nobody thought about ventilation because it happened by accident. Since then most have been insulated, often several times, with the insulation pushed enthusiastically into the eaves where the airflow used to come in. The result is a cold sealed loft above a warm house, which is the standard recipe for condensation. This is why so many houses of this type develop damp problems that are nothing to do with the roof covering at all, and why replacing the covering without addressing airflow can leave the owner with the same wet loft and a much lighter wallet.

The party wall and the shared stack

A semi shares one wall and frequently one chimney stack with the house next door. That means shared responsibility for the stack, and it means the two roofs meet at a junction that has to be right. Where one half of a pair has been recovered and the other has not, that junction becomes the weak point, and where one owner has changed the covering to something with a different profile or thickness, the meeting of the two can be genuinely awkward to weatherproof. If the neighbouring half has recently been done and yours has not, it is worth asking who dealt with the junction and how.

What to look at from the front garden

Look along the hip lines for missing or displaced mortar and for hip tiles sitting out of line. Look at the ridge for the same. Look at the bay roof, which you can often see from an upstairs window of your own house, for standing water, moss or a lifted edge at the wall. Look at the main slopes for tiles that have slipped, cracked or gone porous and mossy. Compare with the other half of the pair and with the neighbouring semis, since these were built as a set and differences between them are informative. And look at the verge at the gable end if there is one, since that is the most wind exposed line.

The sensible order of work

If the covering is sound and the problem is at the junctions, then hip and ridge rebedding, a bay roof renewal and any flashing repairs are a coherent package that can be done in one visit with one set of access costs. If the covering itself is failing, that changes the conversation to a recover, at which point the hips, ridge, bay and ventilation should all be dealt with as part of the same job rather than piecemeal afterwards. The mistake to avoid on a house of this type is spending on the main slopes while leaving the bay and the junctions, because those are where the water was actually coming in.

The garage, the porch and the other small roofs

Houses of this type accumulated additions: a garage to the side, a porch at the front, a canopy over a door, a later extension at the back. Each has its own small roof, usually flat, usually built at a different time by a different trade to a different standard, and each has a junction with the main building. Collectively these minor roofs cause a disproportionate share of the water problems on a house of this age, precisely because none of them feels significant enough to inspect. A detached garage roof leaking harms only what is stored in it, but a porch or a side extension puts water into the house walls. When a roof assessment is being carried out, it is worth asking specifically that these smaller surfaces be included rather than only the main roof.

Frequently Asked Questions

How long does a 1930s roof last?

The tiles themselves may still be serviceable, but the mortar bedding at ridges and hips typically needs attention every twenty to thirty years, so a roof of this age is on its third or fourth cycle. Original coverings from this period are at or beyond the point where they should be properly assessed rather than assumed sound.

Why do hipped roofs have more problems?

Because they have more junctions. A hip is an external angle where two slopes meet, covered by mortar bedded hip tiles, and a hipped roof carries considerably more of that bedding than a plain gable roof. Junctions fail before plain slopes do, so more junctions means more maintenance.

What is the roof over my bay window made of?

On a house of this age, most likely lead, felt or a later replacement in a modern membrane. It is usually flat or very shallow, often has no gutter, and is frequently the surface that has never been touched since the house was built, which is why it is such a common source of damp above the front room.

Should I insulate the loft more?

Insulation is worth having, but on a house of this era the ventilation has to be considered alongside it. These lofts were never designed to breathe deliberately, and insulation pushed into the eaves blocks the airflow that was happening by accident. Adding depth without a clear air path at the eaves commonly produces condensation.

My neighbour has had their half recovered. Does that affect me?

It can. The two roofs meet at a junction that has to be weatherproofed, and where one side has been changed to a different profile or thickness that junction becomes the awkward part. It is worth asking who dealt with it and how, particularly if damp has appeared on that side since.

Is it worth recovering the whole roof or just repairing?

It depends on whether the covering or the junctions are failing. Sound tiles with failed hip and ridge mortar is a repair package. A covering that is porous, cracked or shedding is a recover, and at that point the hips, ridge, bay roof and ventilation are best dealt with in the same visit rather than separately afterwards.