How Much Does it Cost to re-roof a house?
A house has a very clever trick of keeping you and your family warm and dry. But it isn’t magic. Of course it isn’t magic. It’s the culmination of millennia of building knowledge and materials science. As with everything in life, one of the most important aspects to a long life is maintenance. A roof by its very nature is a robust structure designed to reliably do at least two main jobs, for a long time; it is not unreasonable to expect a well designed and constructed roof to do its job for 30 years or more before a major inspection is necessary. However, people often assume that the need for regular thorough inspections means that a more frequent but less comprehensive inspection is not necessary. This is a mistake!
The first, and most important job of a roof is to keep water out of the building below it. Failure to do this will add up to result in a very high cost to re-roof a house when it eventually needs doing. Water is an incredibly invasive material – just think of easy it is to get everywhere in the kitchen or the bathroom! Of course, water generally doesn’t get sprayed around from a tap on the underside of a roof, it generally comes straight down in the form of… yes, you guessed it: rain! Occasionally the rain will be blown sideways by the wind, but this is something which is easily coped with by a good roof.
You will almost certainly be aware already that there are two main types of roofs: pitched, and flat. A pitched roof is the kind which has slopes running from a peak, down to the guttering, providing rain management, whilst a flat roof is just as simple to imagine… it’s flat!
These two differences are very substantial though, and the correct materials must be used when constructing one or the other. Many so-called flat roofs are in fact not flat, but have a shallow pitch on them to facilitate water run-off. These types of shallow-pitched roofs are common on garages, sheds and some more modern houses, and can be easily made from the same materials as the more traditionally pitched roofs: overwhelmingly that material will be a wooden structure with some sort of tile for steep pitched roofs, and usually a bitumen coated paper material for shallow pitched roofs.
It is important to understand that a shallow pitched roof will have more chance of water pooling on it for a greater length of time than a steep pitched roof, and so the ability of water to find even the smallest of holes and drip through in to the living space below increases – this is why a waterproof fabric-like material such as the bitumen coated paper is used: it is waterproof!
Advances in materials technology have provided the roofing industry with new materials which far exceed the capability of the traditional bitumen paper, and really, that is something which shouldn’t be used on a home nowadays. Newer materials based on rubbery plastics (bitumen is a by-product of oil refining) have the ability to self-heal smaller holes or tears which might occur from mechanical damage like sharp debris blown in a strong wind, or even careless people walking on the roof in unsuitable footwear. These all add up to the overall cost to re-roof a house.
Truly flat roofs must battle against the very much increased risk of pooling water and its inherent risks by being made of a waterproof material. It is not uncommon for these flat roofs to be made of a special waterproof mix of concrete. Mechanical damage is still something to be concerned with even on a concrete roof – don’t forget a little bit here and there soon adds up to a lot when it happens over a long time period, so it is doubly as important that people in charge of the maintenance of these types of roofs keep an eye out for it on a regular basis.
If we return now to the most common form of roof, the steeply pitched roof, we can learn what a roof needs if we look at how they are made, and what each part used in its construction is expected to do and how it all adds up to the cost to re-roof a house in full.
Firstly, the exterior covering, which is the part we see, must be a waterproof, and strong enough to withstand impacts from debris. Hang on… this sounds very much like the requirements for the flat roofs I hear you say. Yes! They are! But in a crucially different way. A pitched roof uses gravity to rid itself of water – it runs off quickly, and gravity being gravity, the water only runs downwards. On the rare occasion that a sustained wind blows rain ‘up’ the roof, it’s construction helps to stop any significant amount of water from sneaking under the tiles or slates. Saving on future imminent repairs being needed plus it helps to reduce the cost to re-roof a house.
The tiles then, do not have to be large enough to cover the whole roof in one unbroken piece – that would be impractical to say the least. The pattern of tiles or slates on a roof – staggered – is used for this reason. One tile sits over the joint of the two below it. In turn, that joint is laid over the middle of the tile below them. It is in this manner that an effectively waterproof roof can be made without actually being technically water proof at all! Imagine being the first person to realise and implement this idea…. They must have felt very satisfied with themselves!
Another cunning aspect of pitched roofs is that anything whipped up in the air which falls on it is more likely to be glancing blow, rather than dead-on straight into it at 90 degrees to its slope, this effectively makes the tiles ‘stronger’ (OK, they aren’t actually stronger in reality, but in technical terms, any impacting object is much more unlikely to be perpendicular to the roofs plane and so the energy absorbed is going to be less, and so the tile has a lower chance of sustaining damage).
Under the tiles there will be a wooden structure to… hold it up! Yes, I know… This structure must be strong because the tiles are heavy. Typical examples include cement fiber slates at about 20 kg, Welsh slate at about 30 kg, all the way (weigh?!) up to clay tiles at a whopping 60 kg*! And that is PER SQUARE METRE! A fairly normal house might have a roof foot-print of say 7 metres by 5 metres, with a hight of 2 metres. By the magic of maths we can calculate that equals just about 40 square metres, multiplied by 60 kg, giving us 2,400 kg. Two point four tonnes! By comparison, a Ford Focus car weighs about 1,350 kg. These can be be quite expensive and run into a large % of the actual cost to re-roof a house.
Clearly then, this wooden structure needs to be strong to support the weight of the roof itself, and to be durable – to last a long time. Some movement of the wood is to be expected over longer periods of time, most notably a slight bow in the roof line which you may have seen in older buildings. This is fine so long as the bow isn’t too dramatic and doesn’t prevent the staggered tiles or slates from fitting over themselves properly, which brings up neatly back round to the need for inspection!
A part of the roof which should be visually inspected on an annual basis are the eaves. This is the part which hangs over the wall, and usually you will find the guttering attached to the fascia board – the outward facing part of the eaves. The underside of the eaves may stick out from the wall by only a few inches, or they might be a bit more substantial, and even have some ornate decoration.
Because they are usually wood uncovered by the tiles or slates, they are exposed to more weathering than the wood under the slates, and will be subject to higher rates of wear from airborne debris, and from insect, bird, and small mammal attempts to get past in to the nice warm, windless inside! It is a good idea to make sure that the eaves are at least painted to protect the wood, and in some situations, a tougher covering of durable plastic or even metal can be used.
A very important thing to note about eaves is that they may have ventilation slots in them to provide air circulation for the roof space – these vents must NEVER be blocked off. They should have some sort of suitable grill on them to permit air circulation, but prevent access to wildlife.
“But hold on! Air circulation in the roof space? You said that a good roof will provide insulation, how can that be if there is free air circulation with the outside?” Excellent question! And have a gold star for paying attention! If, very simply, you think of the roof as a hat for your house, then the boxes of the room directly below the roof will require insulation to keep warmth in, cold out, and to stop uncontrolled room ventilation (also known as a draught!) The insulation should be fixed appropriately to the upper side of the room’s ceiling. This still leaves plenty of space within the roof for air circulation.
“But why is air circulation important?” Ah, well, that’s because the space is subject to big changes in temperature and humidity – this is to be expected, and if the roof was sealed from air circulation, hot, humid days, and rainy days, would slowly build up the humidity in the roof space as airborne moisture propagates through everywhere. This is a normal process, by the way, so don’t be alarmed. But what happens when the temperature drops as the night comes round? Moisture will condense out of the air and kick-start mold growth. You don’t want a moldy roof space. The spores of the mold WILL spread through your house, and cause problems for anyone with breathing issues plus increasing the cost to re-roof a house. Even if you have none, you likely will experience sneezing and itching – mold spores are a respiratory tract irritant.
Another problem with moisture condensing out of the air is that it will moisten the insulation intended to keep the rooms below warm (or cool, in summer!) and have a detrimental effect on the insulation’s efficiency. So all in all, it’s a really good idea to make sure the roof space is properly ventilated!
So now we have explored the different jobs that a roof has to do, and the things it needs to do these jobs properly, I am sure you will understand that your roof shouldn’t just be neglected as something that will cost a lot to fix when it goes wrong, but as an actively managed part of your beloved home. To recap, an annual visual inspection of your roof – looking at the tiles and the eaves for any slipped / broken / missing tiles, and a good seal for the eaves to stop things getting in but also clear ventilation grills can help you to identify the need for any remedial action needed early on, nipping problems in the bud, and saving you money on the cost to re-roof a house. Perhaps you could even take pictures of what you find to keep track of things year-to-year so you don’t have to rely on distant memories.
Every 5 or 10 years, a more thorough inspection can be undertaken for little cost by a professional, who will get on to the roof itself and look for the integrity of joins and seams and all the parts which are not easily viewable from the ground. Of course, a professional should be consulted any time you notice anything visually from the ground – maybe a severe storm has lifted tiles, or blown something on to the roof and damaged tiles or slates.
A roof is very important, and is a prime example of where you have to be careful not to be “penny wise but pound foolish”!
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