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If you are looking for information on insulating basement walls, we put together a guide on the cost of doing the job. We included 4 free contractor quotes.
Basements are a very common feature of houses in the United States and Canada but not so common in UK except in older houses which tend to have a cellar. For those that don’t know, a basement is part of the house that is below ground. At its lower end you will find the foundations and at the upper end you will find the flooring joists of the ground floor.
Do we need a basement? There has long been a heated discussion about the benefits and disadvantages of building a house on each of the three common foundation types:
The fact of the matter is that they each have their own advantages and disadvantages as long as each method is built properly and to the building codes. No matter which method you prefer, no-one can argue that basements aren’t handy and not only provide a lot of storage space but if waterproofed, insulated and heated properly they can significantly expand your living accommodation, even if it is just as a den, family gym or cinema room.
Before central heating became commonplace in North America, most cold climate homes were equipped with a basement or a cellar. This was because this room was the only one that would stay above freezing point during the frigid winters. It was basically insulated from the freezing outside air by the surrounding ground. This meant that homeowners could safely store harvested vegetables such as potatoes, carrots, turnips and so on without worrying that they would be spoiled by frost.
This may not be so today as most, if not all houses are equipped with some form of heating and there is no longer the risk of fresh food succumbing to the cold.
So why do people still have basements built under their homes? Well the simple answer is that they are still very handy:
Repairs to the household plumbing are easier as there is plenty of access to the underfloor area.
A basement is the perfect location for household mechanical equipment such as a furnace, water heater and air conditioning unit. If the basement is properly finished then all this equipment will be safe within the house’s thermal envelope.
Air conditioning ducts are very simply installed within the basement. There is plenty of room for the contractor to walk around and stand upright while installing and maintaining ducts. This means that work can be completed faster and to a higher quality.
When dealing with hot water it is much better if all distribution pipes and ducts are kept as short as possible to reduce thermal losses. A furnace or water heater can be situated as close to the centre of the house as needed to keep the pipes as short as possible.
If you live in an area with a high tornado risk, the best place to build a safe room is in the basement.
Most basements extend well below the frost line so they can require less heating than the rest of the house in winter.
If you have a small building lot as well as height restrictions in your neighbourhood, a basement can give you extra living area if you need to expand.
Today’s article will be focussing on the methods used to insulate the basement from the outside world so that it can be used as a functional part of the family home.
Ok. Just think on this one for a while.
In the middle of winter on a really cold day the temperature outside your house is about -5°C (about 23°F). However the ground temperature below the frost level is about 10°C (about 50°F), while the temperature in your home will be about 20°C (68°F).
We all know that heat travels from warm things to cold things so the warmth in your house will tend to migrate to the cooler areas, namely the attic and the basement. Any heat that arrives in your basement will slowly bridge the foundation walls and try to reach the cold ground outside. This is money down the drain so it would make sense to insulate your basement if it is possible.
Before we talk about insulation let’s talk about something else; the moisture. Yes that’s right; basements are usually damp so before any insulation takes place you have to stop the water from coming in. There are a number of ways to do this:
✓ Make sure you have wide overhangs on the roofs and gutters discharging rainwater to pipes that deliver the water a long way from the foundations.
✓ Before laying the concrete basement floor, lay a four inch thick layer of crushed stone. This will act as a capillary break keeping the moisture away from the concrete. The crushed stone will need to be vented to disperse the radon gas that will attempt to seep through and into the house.
✓ On top of the crushed stone you need a layer of rigid foam to insulate the concrete from the ground.
✓ On top of the rigid foam layer (and directly beneath the concrete slab) you need a layer of heavy duty polyethylene damp proof membrane to perform as a vapour barrier.
✓ You need a 4” diameter pipe running through, and perpendicular to the foundation wall to allow any build-up of water at the crushed stone to discharge to the exterior footing drain.
✓ Use a bitumen based paint to act as a capillary break between the concrete footing and the foundation.
✓ Around the outside of the footing you need a perforated land drain pipe sunk in a trench filled with crushed stone to divert any build-up of water to a suitable soakaway area.
✓ Apply a suitable bitumen compound to the outside of the concrete foundation walls.
✓ Apply dimple mat to the outside of the foundation walls or backfill around the walls with a free draining crushed stone.
✓ Add a closed cell foam seal between the top of the foundation walls and the mud sill to act as a capillary break.
✓ You have probably noticed that all of these dam proofing methods I just mentioned all require you to have access to the exterior face of the basement walls (the foundation walls). If you have access to waterproof the exterior then it is best to insulate the exterior as well.
Although waterproofing and insulating the exterior is ideal as it keeps the concrete within the buildings thermal envelope, it isn’t always feasible to do this. If this is the case then you will have to waterproof the interior walls and floor before adding insulation. If you possibly can, do as much as is feasible to reduce the amount of water in contact with the exterior face of the foundation walls.
As stated in the previous section it is ideal to waterproof and insulate the outside of the foundation walls (the basement walls). This is however only really feasible if you are building a new basement or if you have access to the exterior face of the basement and can backfill.
For most of us however, we will only have access to the internal face of the foundation walls and the upper face of the concrete floor slab. Whether you think that the cost of excavating the outside foundations is worthwhile or whether your budget can only manage the interior is for you to decide. Before you consider which choice is worthwhile just look at the comparison between insulating the exterior or the interior.
✓ Maintains the concrete within the thermal envelope of the house.
✓ Protects the damp proofing layer from damage during backfill of crushed stone.
✓ Allows an unbroken layer of sprayed rigid foam onto the external face. If you are building a new house then you can continue with the layer all the way to the eaves providing an unbroken seal.
✓ Allows more space inside the basement.
✓ Easier to insulate the rim joist area using external rather than internal insulation.
✓ You don’t need internal studs and drywall.
✓ You don’t need to cover up the concrete walls so can be inspected for cracks and damage at any time.
✓ The insulation work can be done after the house is dry. If done externally then there is always a rush to backfill the foundations.
✓ It is easier to provide a continuous insulation layer from the floor to the walls.
✓ The interior insulation does not need protection from the weather if part of the basement projects above external ground level.
As stated earlier, most of us will be trying to insulate a ready-built existing basement. We cannot get to the outside wall to waterproof it or to insulate it. So what do we do?
Before you cover up your concrete with damp proof paint, bitumen or with insulation you need to ensure that the concrete is in good condition and doesn’t have a problem with water ingress.
Dealing with water leaking into your basement is a topic for another article as it is beyond the scope of this one. Let’s just say that if your basement walls become wet in the springtime or after you have had a heavy rainfall then you must not insulate them until you have sorted out the water problem.
There are a few things you can try which may work but other than that you will need the services of a properly qualified and licensed contractor.
Possible solutions include:
✓ Adjust the slope of the ground around your house so the gradient slopes away from the walls on all sides.
✓ Make sure your guttering discharges into downpipes that convey the water away from the foundations.
✓ Excavate around the walls down to footing level and install footing drains.
✓ Install a French drain around the basement and connect to a sump equipped with a sump pump.
✓ Whatever happens you will need to repair any cracks or holes, reduce the amount of water affecting the exterior of the walls and then waterproof the interior of the walls.
✓ If your foundation walls are made from poured concrete then you are in luck, as long as no water is leaking through it is perfectly feasible to insulate the walls with a variety of types of insulation. If however you have stone or brick and mortar walls unfortunately you won’t be able to insulate them with foam slabs. The only way is to use closed cell spray polyurethane foam.
The best way to insulate the internal walls of a basement is to apply rigid foam insulation and attach it directly to the concrete. The best insulation materials are:
Rigid foam slabs can be connected directly to the concrete walls with a foam compatible adhesive or with special mechanical fasteners. Whichever method you use the prime objective is to prevent interior air from touching the cold concrete surface otherwise condensation will occur followed by mould growth and rot. It is for this reason that solid foam is preferred over fibreglass rolls and batts or over cellulose. If spray foam is used then the foam will naturally adhere and the concrete will be completely enclosed. If rigid foam slabs are used then the joints between slabs and the gap at the slab perimeter will need to be sealed using caulk, adhesive or canned spray foam.
Foam is usually flammable so building codes require most types of foam to be covered by gypsum drywall to provide a fire break. For this reason the foam should be enclosed in studwork and gypsum board. Most builders will add 2”x 4” timber studwork onto which the gypsum drywall is attached. The studs provide a ready-made chase for electrical cables and water pipes and the gaps between the studs can be filled with more foam insulation. You may be tempted to attach a polyethylene damp proof membrane between the studs and the drywall to act as a further vapour barrier. Do not do this as it will prevent any moisture that gets behind the foam from drying to the interior.
As mentioned previously the use of fiberglass batts, mineral wool batts, cellulose or any other air permeable insulation is not a good idea.
When this type of insulation is used there is nothing to prevent the warm moisture-laden air from permeating the fibers and coming into contact with the cold concrete wall. The water vapor will subsequently condense against the cold surface and provide ideal conditions for mold growth and rot. The best types of insulation are the closed cell spray foam and rigid foam batts. The thickness of foam needed in your climate zone to comply with the building codes will depend on the R-value per inch of the foam. (The R values for the climate zones have been tabulated in the next section).
According to the 2012 International Residential Code, the required types of insulation in basements in Climate Zones 3 and above are to use rigid foam (not fibreglass). The manufacturer of the foam will tell you the R value per inch of the foam (it will be on the wrapping) so you can work out the minimum thickness of foam required to comply with the building codes.
|Required R values for basements according to building code|
|Zone 4 (except Marine Zone 4)||R-10|
|Marine Zone 4||R-15|
|Zones 5, 6, 7, 8||R-15|
The factors affecting the cost of insulating your basement will depend on the following:
✓ Whether the insulation is exterior or interior. Exterior work will require the hire of excavators and significant upheaval of the ground around the house as well as backfill and landscaping afterwards.
✓ The dimensions of your basement. A large basement will require more work and insulation than a smaller one.
What other work is necessary before insulating; waterproofing, repairs to the walls, laying concrete floor slab, external ground and drainage work.
✓ What type of insulation you choose. The choice with basements is between rigid foam slabs and spray application foam. Both of which have their pros and cons.
✓ What climate zone you live in will govern the thickness of insulation needed. If you are insulating the interior then the thickness of foam will affect the amount of living space you lose.
✓ The foam is flammable so it must be covered up with a fire break before the room can be used. This is normally done by building a freestanding stud wall and applying gypsum drywall boards to the studs. This is another added expense.
✓ Depending on the extent of the work you intend you may have to employ an architect or a structural engineer. For a relatively small job you may just need a basic sketch of the dimensions. If you have a large basement with services being installed, a new concrete floor slab or any work on the exterior you will require proper architect’s drawings giving levels, specifications of materials and required dimensions. Not only will your contractor require these to work with, you will also have to submit plans to the authorities when applying for permits.
✓ You will need electricity and probably some form of heating in the new insulated basement so will require the services of a plumber and an electrician together with the materials they need to do the job.
✓ Depending on the work needed to be done you will require various permits. These will cost extra and will depend on where you live.
✓ Whether you choose to hire a contractor or DIY. If you do it as a DIY project then you will not be spending on labour, only your own time.
✓ What access you have to the basement. It may be that the basement has never had any improvements done and the method of access may be by trapdoor and ladder. If this is the case then you will have to allow for suitable access to be built before it is safe for anyone to enter. Stairs and a doorway at the top would be essential as is a suitable concrete floor with damp proof course.
✓ Time of year. If you have problems with ingress of water then the waterproofing will need to be done during the summer months when there is less groundwater to disrupt proceedings.
✓ Locality. Where your house is located will have a bearing on how easy it is to do the work. If you live in a rural setting the work will be easier than if you live in the middle of a city. Both locations have their own problems and advantages that need to be considered and allowed for in the costs.
✓ Materials. Always ensure the wood that is being used to build the stud walls is pressure treated to prevent rot. Use rustproof fixings and take care when fixing the studs to any existing surfaces. You don’t want to breach any waterproof membrane that has been fitted previously.
The costs of materials and contractor labor will vary depending on where you live and what quality materials you choose. Materials can be purchased online, from specialist building supply merchants or home improvement stores and the price will vary accordingly.
Always ask for quotations from more than one supplier and don’t forget that building supply merchants are geared up for selling to contractors so you may get preferential rates for buying in bulk.
|Costs of hiring professionals|
|Carpenter||$70 to $100|
|Electrician||$65 to $100|
|Plumber||$45 to $150|
|Cost to waterproof a basement|
|Typical range||$2,000 to $6,500|
|Cost of some materials and services|
|Drywall panels||$10 to $20 per 8’x4’ panel|
|Closed cell spray foam kit||$900 for 600 square feet|
|External damp proofing||$3 to $6 per square foot|
|Exterior cement waterproofing||$1,000 to $2,000 depending on area|
|Interior waterproofing||$500 to $1,000 depending on area|
|Waterproofing paint||$40 to $130 per gallon|
|Permits||$100 to $3000 depending on type|
What types of contractors will be required to do the work for you?
✓ If you need to work on the outside by installing land drains or crushed rock backfill you will need licenced ground workers and people qualified to use mechanical excavators.
✓ Repairs to foundation walls will need bricklayers, masons or concrete layers.
✓ Waterproofing will need specialist waterproofing contractors or bricklayers.
✓ Fitting insulation will need specialist insulation contractors, bricklayers or carpenters. Spray foam applications will always require specialist contractors.
✓ Internal insulation can be done by carpenters or drywall contractors.
✓ Studwork and drywall can be done by carpenters or specialist drywall contractors.
✓ Laying a concrete slab floor will require a general contractor, concrete layers or specialist flooring contractors.
Before deciding on whether you are going to do the job yourself or hire a contractor you should get advice from an independent professional. We say independent because you don’t want the professional to think he or she is going to get a lot of work from it and so produce a biased report. All you require is a report outlining the:
You will have to pay for the report, most professionals won’t do work for free, but if you carry on and use the person as the main contractor there is a good chance that you will be credited for this amount against the final invoice. The amount of work that the report says is required will also give you a good idea whether it would be wise to hire a professional or do it yourself.
The right contractor is worth their weight in gold. You want someone who is value for money, can work quickly and efficiently and who produces minimal waste.
Contractors who specialise in groundwork, insulation and damp proofing are needed for this kind of work. When you look for the appropriate contractor there are ways of making sure you end up with someone who is responsible, honest and professional. Just follow these simple steps:
✓ Ask around among your family, friends, and neighbors for recommendations.
✓ Use social media. It is amazing how easy it is to find a good contractor by listening to the various forums.
✓ When you make your initial approaches to the local city planning department to find out what permits are required also ask if they can recommend suitable contractors. Even if they are unable to give a favorable reference they may be able to tell you who has a reputation for bad workmanship.
✓ Ask at the local building supply merchant. Not only is the staff aware of all the contractors in the area but often professionals will leave business cards on the counter.
Remember that everyone’s standards are different and what is acceptable for one person may be unacceptable for someone else. Also, remember to ask the contractor about your specific job, he may be good at some tasks but not others. It doesn’t matter how many favorable references a person has, it is up to you to decide whether you will be happy working with a specific contractor.
Once you have decided on a shortlist of prospective contractors it would be wise to ask a series of questions to see which one is most suitable.
How long have you been trading? You can often get a good idea of the person’s competency by taking note of how they answer this question.
How many basements have you worked on? I know this one sounds obvious but basically, it is the clincher and you need to know this. You are trying to ascertain whether the contractor knows the procedures, regulations and building codes and also how they would go about doing the job.
Have you the correct insurance? A reputable contractor will have the correct insurance. Make sure they have insurance to cover breakages, bad workmanship, injury and death to themselves and your family.
Are you licensed? A good contractor will be licensed to work in your area. Make sure their license covers the work you intend having done.
Do you offer guarantees and warranties? A reputable contractor will offer some kind of after-sales service in case the work needs doing again or in case the materials fail within a certain length of time. Check the materials he intends to use are of a recognized brand and is suitable for the task at hand.
Can you organize permits? A contractor who is licensed and recognized by the local planning department will have no problems sorting out the permits. They can be difficult to understand for the ordinary person so someone who is used to applying for them would be advantageous.
When can you start work and how long will it take? This is vital to know as you should choose a contractor who can fit in around you. Remember that a good contractor is unlikely to be able to start next Monday! There are just too many things that will need organizing:
What times do you work, what are your core hours? You want the work to be finished as quickly as possible and with as little upheaval as possible. You will need reassurance that the contractor will put in a full day’s work and won’t disappear to the pub or the beach when he feels like it.
Can you supply any references? Ask to see some examples of the contractor’s work before you make a decision. You will want to see the quality of his work for yourself and speak to previous satisfied customers. Get three or four references and go to see them. You can ask:
Can the contractor supply a full estimate or quotation? You will need to know what you are paying for so the written quotation should include:
What is the customer expected to supply? Is the customer expected to supply electricity, water, access and parking, lighting? Have this written down in the contract so that valuable time and money isn’t wasted at the beginning of the job.
The question of whether to hire a contractor or do it yourself is one that only you can answer. You must realize that you will be spending a lot of money on this job and you, therefore, need the work done properly. Playing around with your house foundations is not advised unless you know exactly what you are doing. If you decide to waterproof and insulate the exterior of the basement then excavation will be required. If you decide to lay a concrete slab floor in the basement, you will need to dig out the existing packed earth and may expose the foundations. Excavating around the footings without proper precautions can jeopardize the integrity of your house, costing you a lot of money.
The main advantages of using contractors include:
✓ Specialist knowledge.
✓ Skill set.
✓ The main advantages of doing the work yourself include:
✓ Not so expensive.
✓ Personal pride.
✓ Ability to change your mind easily.
We have talked about what needs to be done when turning your basement into a habitable room by insulating it. There are two ways one to do this. One is from the outside and one from the inside. Unless you are building a new house, most people will choose the ‘insulating the inside’ option.
Whichever you choose, as long as you do the job properly and follow all the building codes you will finish up with the basis for a very useful addition to the living space in your home.
We hope you have come away with some new information from this article and that it will prove useful if you ever decide to insulate your basement. Thank you for reading.