Roof replacement

A roof replacement means different things to different people. Some think only of a new covering, others of a complete renewal from the rafters to the gutters. On the pitched roof of a family house, a thorough replacement usually covers the whole build-up above the roof structure: the old covering, the battens, the underlay or breathable membrane, counter battens, new battens or boarding, the new covering and all the sheet metal details. Gutters, downpipes, eaves drip flashings, chimney flashings, valleys, the ridge and the verges belong to the job as well.

The roof structure itself, the timber rafters, purlins and wall plates, is not replaced automatically when the covering is renewed. However, an uncovered roof is the only moment when the structure can be inspected properly, repaired and strengthened if needed. It is also the best time to add insulation if the loft is lived in or is going to be converted.

Not every old roof needs replacing. A few cracked tiles, a loose ridge tile or a leaking chimney flashing can be repaired locally. Replacement makes sense when problems keep appearing in several places or when the covering is worn out across the whole surface.

Typical signs that a roof has reached the end of its service life:

• tiles crumble, flake or soak up water and crack in frost,
• metal sheets are rusty over large areas, not only at the edges and around the screws,
• water comes in at different places and a new leak appears after every repair,
• there is no underlay below the covering and snow or rain blows into the loft,
• battens are rotten or sag under the covering,
• the roof is made of asbestos cement slates or corrugated sheets that are weathered and covered with moss.

With concrete and clay tiles it often happens that the tiles themselves would last longer, but there is no secondary waterproofing under them and the battens are finished. In that case tiles in good condition can sometimes be taken down, sorted and laid again. With old asbestos cement, worn fibre cement slates and badly rusted metal this makes no sense.

The roof structure carries the covering, the battens, snow and wind. When replacing the roof it is therefore important to know whether the new covering will be much heavier than the old one. Clay and concrete tiles weigh roughly 40 to 50 kg per m², a metal roof only about 5 kg per m² and stone-coated steel tiles around 7 to 8 kg per m². When changing from metal or light asbestos cement sheets to tiles, the load on the structure should be checked by a structural engineer. The opposite direction, from tiles to metal, makes the roof lighter.

Once the roof is uncovered, the structure is inspected along its whole length. Inspectors look for rot at the wall plate and the eaves, where timber gets wet most often, damage from wood-boring insects, cracked or bent rafters, loose joints and traces of old leaks. Damaged members are replaced or doubled, and sound timber is treated with a preservative. If the roof sags so much that it is visible to the naked eye at the ridge or across the roof plane, it should be assessed by a structural engineer before the covering is ordered.

Prices of carpentry work such as fitting rafters, replacing a roof structure or treating timber are described in the article Carpentry construction.

Tiled roofs

Concrete and clay tiles are among the most common roof coverings in Europe. They are heavy, quiet in the rain and long-lasting, and they reduce noise and summer overheating of the loft better than lighter coverings. On the other hand, they need a properly sized roof structure and a steeper pitch, and laying them is slower. Every tile model has a minimum pitch set by the manufacturer, which depends on the tile profile and on the secondary waterproofing beneath it. On low-pitched roofs tiles often cannot be used at all, or only with an upgraded underlay.

Metal roofs

Metal is light and quick to install. By shape it is divided into metal tile sheets, trapezoidal profiles and standing seam roofing. Metal tile sheets and trapezoidal sheets are screwed onto battens, while standing seam roofing is laid on full boarding. Metal copes with lower pitches, but it is noisier in the rain and condensation can form underneath. That is why it is laid over an underlay with a ventilated gap, and some products also have an anti-condensation coating on the underside. Steel with a coating, aluminium, zinc and copper are all used, with very different prices and service lives.

How to decide

• with an old roof structure and a light original covering, metal is often the safer choice,
• with a lived-in loft directly under the roof, the quietness and thermal mass of tiles are appreciated,
• on low pitches the minimum pitches in the manufacturers' technical data sheets decide,
• in a conservation area or a municipality with binding design rules, the type and colour of the covering may be prescribed.

Below the covering there should be secondary waterproofing, today most often a breathable membrane laid directly on the rafters or on boarding. Counter battens are nailed onto it to create a ventilated gap, and only then come the battens or boarding for the covering. Air flows from the eaves to the ridge and carries moisture away. At the eaves a ventilation grille protects against birds and insects, at the ridge a ventilated ridge roll is used.

A roof replacement is the ideal moment to insulate. If the loft is lived in, insulation goes between and below the rafters and is closed from the inside with a vapour control layer with taped joints. If the loft stays unheated, it is often simpler to insulate the ceiling below it, for example with blown insulation. In many European countries there are public grants or tax relief for roof insulation, often only when the covering is replaced together with insulation. Check the current conditions on the official portal of the national or regional energy agency before signing a contract.

Many houses from the second half of the 20th century have roofs made of asbestos cement slates or corrugated sheets. As long as the covering is intact, fibres are not released. The risk arises when sheets are broken, cut, drilled, pressure-washed or removed by untrained people.

In the European Union, work with asbestos is strictly regulated. Asbestos cement roofing may only be removed by specialist firms with the required authorisation or training, which notify the competent authority before work starts. The waste is hazardous and must be taken to an authorised facility. Neither a homeowner nor an ordinary roofing crew should touch an old asbestos cement roof. If you are not sure what your roof is made of, have a sample analysed by an accredited laboratory before any work starts. The procedure, obligations and price of removal are described in the article Asbestos and asbestos cement removal.

A roof replacement is work for roofers and sheet metal workers, often together with a carpenter for repairs to the roof structure. In many countries roofing is a regulated trade, so it is worth checking that the firm is registered, has liability insurance and gives a written guarantee for the covering and the details. Ask for references from similar roofs and for a quote broken down into dismantling, carpentry, underlay, covering, flashings, scaffolding and waste disposal.

Check with your local authority whether replacing the roof needs a permit or a notification in your case.

On a typical gable roof of a family house, the replacement follows a well-established order. It is important that the roof is never left open overnight without temporary cover and that the work is carried out in sections according to the weather.

1. Erect scaffolding or secure work at height and place a skip for waste.
2. Dismantle gutters, downpipes, ridge tiles and the flashings of the chimney and verges.
3. Take down the old covering and battens, sorting tiles that can be reused.
4. Inspect and repair the roof structure, replace damaged members and treat the timber.
5. Lay the breathable membrane, or boarding with secondary waterproofing.
6. Fix counter battens and new battens at the spacing required by the covering, or full boarding for standing seam metal.
7. Fit eaves drip flashings, gutter brackets and ventilation elements at the eaves.
8. Lay the new covering including valleys, ridge and verge elements.
9. Flash the chimney, roof windows and penetrations.
10. Fit gutters, downpipes and snow guards.
11. Clean up around the house and remove the waste.

To give an idea of the budget, here is an indicative calculation for a typical family house with a gable roof of 150 m². It assumes stripping old tiles, a new underlay and a new covering. The calculation covers labour only according to the NUMIQ price list, including minor consumables, without the covering, timber, membranes, sheet metal and other main materials, without scaffolding, waste disposal and repairs to the roof structure.

Option A: new tiled roof

• stripping the old tile covering 150 m² × €8.50 = €1,275,
• removing the old battens 150 m² × €2.70 = €405,
• laying a breathable roofing membrane 150 m² × €2.90 = €435,
• fixing counter battens 150 m² × €3.90 = €585,
• fixing new tiling battens 150 m² × €5.50 = €825,
• laying clay or concrete roof tiles 150 m² × €30 = €4,500,
• removing old gutters and downpipes 49 m × €4.50 = €220.50,
• fitting eaves gutters 25 m × €9.50 = €237.50,
• fitting downpipes 24 m × €9 = €216,
• fitting eaves drip flashing 25 m × €10 = €250,
• flashing the chimney with sheet metal 4 m × €22 = €88.

In total the labour comes to roughly €9,040, or about €60 per m² of roof. Prices vary by region and city, and they are usually higher in large cities and in tourist regions.

Option B: standing seam metal roof

With standing seam metal the battens and tile laying are left out. Instead, the roof is boarded with OSB or timber boards for €9.50 per m², and the standing seam covering costs €19 per m². For the same roof the labour therefore comes to roughly €7,990. If the original covering is metal, stripping it costs €5.80 per m² according to the price list instead of €8.50 for tiles, which means €870 for 150 m².

The calculation really is only indicative. The real price is shifted by the shape of the roof with hips, valleys and dormers, the number of roof windows and chimneys, the pitch, the height of the house and the condition of the roof structure. Materials, scaffolding and waste disposal have to be added to the labour. Old tiles weighing around 40 to 50 kg per m² produce roughly 6 to 7 tonnes of waste on 150 m², which is charged by weight. Demolition work and rubble removal are described in the article Demolition work, all sheet metal items can be found in the article Sheet metal works.

• new covering without checking the roof structure: the new roof sits on a rotten wall plate and starts to sag a few years later,
• heavy tiles on a structure designed for metal: rafters bend and crack,
• missing ventilated gap: water condenses under the metal and drips into the loft,
• pitch below the manufacturer's minimum: in heavy rain and wind water gets under the tiles,
• cheap chimney flashing: sealant instead of overlapping metal cracks and leaks,
• eaves ventilation blocked by insulation: the roof can no longer breathe,
• improper removal of asbestos cement: broken sheets release fibres and the waste ends up in the wrong place,
• roof left open overnight without cover: a storm ruins ceilings and plaster inside the house.

The roof replacement itself is a job for roofers and sheet metal workers. The owner can still do a lot to make sure the work goes quickly and without damage.

1. Clear the loft so that the roof structure and the wall plate are accessible all around.
2. Photograph the roof from outside and inside, especially places with traces of leaks.
3. Find out what the old covering is made of and, if asbestos cement is suspected, tell the firm in advance.
4. Ask for a written quote with a timetable and agree what happens if hidden damage to the roof structure is found.
5. Agree with neighbours and the municipality on space for scaffolding and a skip.
6. Cover belongings in the loft and under the roof with plastic sheeting against dust and dirt.
7. Decide on insulation and roof windows before work starts, as they are difficult to add later.

• the roof structure was inspected and damaged members replaced, and there are photos,
• there is a continuous underlay with overlaps and a ventilated gap below the covering,
• ventilation at the eaves and ridge is open and protected with a grille,
• the covering lies flat, without cracked pieces and fixed according to the manufacturer,
• the chimney, roof windows and penetrations are flashed with metal, not only with sealant,
• gutters fall towards the downpipes and water drains away in a test,
• the firm handed over documents on materials and the guarantee, and for asbestos cement proof of waste disposal,
• the surroundings of the house are clean and free of nails and fragments.