Older houses commonly have cast iron guttering in a deep ogee or moulded profile, carrying more water than the standard modern half-round that replaces it. Fitting a smaller section to a large roof causes overflow in heavy rain, which gets blamed on blockages. Match the capacity and the profile, or use a modern deep-flow or cast-iron-effect equivalent.
- Standard half-round is often smaller than the cast iron it replaces. Capacity, not just appearance.
- Cast iron fails at the joints and the back edge, not usually across the middle. Repair is often viable.
- Ogee profiles fix flush against the fascia and shed water differently from half-round.
- In a conservation area, changing cast iron to plastic may not be acceptable. Check first.
What is usually there
Two things distinguish the roofline on a Victorian or interwar house from a modern one, and both get overlooked when it is replaced.
The material is cast iron. Heavy, brittle, bolted together at the joints with a sealing compound, and painted. Properly maintained it lasts a very long time — there is original cast iron on houses well over a century old still doing its job. Neglected, it rusts from the inside out, the joints weep and the back edge corrodes where it sits against the timber.
The profile is usually not half-round. The common older profiles are:
- Ogee — an S-curved front face with a flat back that fixes directly against the fascia or the brickwork. Very common on both Victorian and 1930s houses, and it has a deep section.
- Moulded or beaded half-round — rounder, but with a decorative bead and typically a larger diameter than modern standard.
- Box or square section — found on larger houses and later work, with high capacity.
- Victorian half-round with a beaded edge — superficially like modern half-round, usually a size up.
- Deep-flow equivalents in cast iron — on bigger roofs where the catchment demanded it.
Downpipes are correspondingly different: often square or rectangular cast iron, sometimes with decorative hopper heads at the top collecting from a valley or a flat roof. Those hoppers are a frequent leak point and are routinely deleted when a roofline is replaced, which pushes the water somewhere it was not meant to go.
Why swapping to standard half-round causes overflow
This is the practical point of the page, and it explains a complaint we hear often: the guttering was replaced and now it overflows in heavy rain, and no amount of clearing fixes it.
Guttering is sized for the area of roof draining into it and the rainfall intensity. A deep ogee or oversized moulded profile on an older house was carrying a given volume. Standard 112mm half-round — the cheapest and most common replacement — carries less.
On a modest roof the difference does not show. On a large roof, a long run with a single outlet, a steeply pitched roof that delivers water fast, or a run collecting from a valley, it shows the first time there is sustained heavy rain.
What makes it worse:
| Factor | Effect on capacity needed | What to do |
|---|---|---|
| Large roof area draining to one run | Much higher | Bigger section, or two outlets |
| Steep pitch | Higher — water arrives faster | Size up |
| Long run with one outlet at the end | Higher | Add an outlet, or fall both ways |
| Collecting from a valley or a flat roof | Much higher | Hopper head, larger section |
| Little or no fall | Water ponds and backs up | Set a proper fall to the outlet |
| Brackets too far apart | Sagging, so it holds water | Correct bracket spacing |
| Outlet smaller than the gutter | Bottleneck | Match the outlet and downpipe |
The last three are installation faults rather than sizing ones, and together they account for a great many overflowing gutters on otherwise adequate systems. A gutter with no fall, or sagging between brackets, holds standing water that then overtops at the low point.
Repair or replace the cast iron?
Cast iron is often more repairable than people assume, because it fails in specific places rather than generally.
Where it fails. At the bolted joints, where the sealing compound has perished and the bolt has rusted. Along the back edge, where water held against the timber corrodes the iron and rots the fascia behind it. At the bracket fixings. And occasionally a cracked section, usually from a ladder, a frost event with the gutter full, or impact.
What repair involves. Taking the run down in sections, wire-brushing and treating the inside, remaking the joints with new bolts and a modern sealant, replacing individual lengths where they are too far gone, and repainting inside and out. The inside is the part that matters and the part most often skipped — cast iron painted only on the visible face continues to rust from within.
When replacement makes more sense. Where multiple sections are cracked, where the fascia and rafter ends behind it have rotted so the whole roofline needs opening up anyway, or where access makes repeated maintenance impractical.
Honest assessment: cast iron repair is skilled, access-dependent work and it is not cheap. What it buys is a system that matches the house and will run for decades more. On a house where the roofline is otherwise sound, it is frequently the better value. Where the fascias and rafter ends have gone, you are into a roofline replacement regardless, and then the question becomes what to replace it with.
The replacement options, ranked for an older house
- New cast iron. Still manufactured in the traditional profiles. Correct in every respect, the most expensive, and heavy enough to need sound fixings. The right answer on a listed building and often the expected one in a conservation area.
- Cast aluminium. Reproduces the profiles including ogee, with the weight and much of the maintenance burden removed. Powder-coated, long-lived, and visually very close. The best compromise for most older houses and considerably cheaper than cast iron.
- Cast-iron-effect uPVC. Moulded to imitate the profile and the joint detail. Better than standard uPVC at a distance, less convincing close up, and inexpensive. Reasonable where budget governs and the house is not in a controlled area.
- uPVC ogee. Correct profile, plastic material. Fixes flush to the fascia like the original and carries more than half-round, so it is the sensible plastic choice on a house that had ogee.
- uPVC deep-flow half-round. Wrong profile but adequate capacity. Acceptable on a rear elevation nobody sees.
- Standard uPVC half-round. The default replacement, the smallest capacity, and the wrong profile. This is the one that causes both the overflow complaints and the elevations that look subtly wrong afterwards.
Whatever the material, the two things to insist on are the right capacity for the roof area and a profile that suits the elevation. A cast-iron-effect system in the correct section beats new cast iron fitted undersized.
Check before you change anything
- Is the property listed? Changing cast iron guttering on a listed building generally needs listed building consent, and plastic is unlikely to be acceptable.
- Is it in a conservation area? Guttering is often a matter of local policy, and an Article 4 direction can remove the right to change it. Worth a call to the planning authority rather than an assumption.
- Do the neighbours still have cast iron? On a terrace or a pair of semis, one house in plastic reads as the odd one out, and it affects both houses at sale.
- Is the fascia and are the rafter ends sound? This is what decides whether you are doing a gutter job or a roofline job. Roofline replacement covers what happens when the timber behind has gone.
- Where does the water actually go? Older houses often have hopper heads, shared downpipes and gullies in unexpected places. Map it before redesigning it.
- Is there a shared gutter run? On terraces the gutter frequently runs continuously across several properties, which makes it a conversation with the neighbours rather than a unilateral decision.
- Is the eaves ventilation adequate? Replacing the roofline is the opportunity to get this right, and the detail is routinely skipped.
What it costs
These are the roofline figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Full uPVC fascia, soffit & guttering (semi) | £1,000–£1,500 | Supply & fit |
| Per elevation (fascia + gutter) | £400–£700 | Front or rear |
| Gutter clean & reseal | £80–£200 | Clears blockages, stops overflow |
| Labour | ~£30/hr | Qualified roofline fitter |
Those figures are for uPVC systems. Cast aluminium typically costs appreciably more and new cast iron more again, and cast iron repair is priced by the day because access governs it. On an older house it is worth getting both a repair price and a replacement price rather than assuming replacement is cheaper.
We price the repair alongside the replacement, and we size the new run for your roof area rather than fitting whatever is standard.
Frequently asked questions
Why does my new guttering overflow when the old cast iron did not?
Because it is almost certainly a smaller section. Older houses commonly had deep ogee or oversized moulded profiles carrying more water than standard 112mm half-round, which is the cheapest and most common replacement. On a large or steeply pitched roof the difference shows the first time there is sustained heavy rain.
What is ogee guttering?
A profile with an S-curved front face and a flat back that fixes directly against the fascia or brickwork, rather than hanging in brackets like half-round. It is very common on Victorian and 1930s houses, it has a deep section with good capacity, and it is still available in cast iron, aluminium and uPVC.
Can cast iron guttering be repaired?
Often, yes. It fails at the bolted joints, along the back edge against the timber, and at the fixings, rather than generally. Repair means taking it down in sections, treating and repainting the inside as well as the outside, and remaking the joints. Painting only the visible face leaves it rusting from within.
Should I replace cast iron guttering with uPVC?
It depends on the house and the area. On a listed building it generally needs consent and plastic is unlikely to be acceptable; in a conservation area it may be controlled. Where plastic is acceptable, choose an ogee or deep-flow profile for the capacity rather than standard half-round.
What is the best alternative to cast iron guttering?
Cast aluminium. It reproduces the traditional profiles including ogee, with the weight and most of the maintenance removed, is powder-coated and long-lived, and is visually very close. It costs appreciably more than uPVC and considerably less than new cast iron, which makes it the usual best compromise.
Why do older houses have hopper heads on the downpipes?
To collect water from a valley, a flat roof or a secondary gutter into the main downpipe. They are a frequent leak point, and they are routinely deleted when a roofline is replaced — which sends that water somewhere it was never meant to go. Map where the water travels before redesigning the system.
Size it for the roof, not the catalogue
We measure the roof area and match the profile before quoting, which is why our replacements do not overflow in the first heavy rain.