What Temperature Should An Attic Be?

Few people give more than a couple of seconds of half-hearted thought to the attic. Your attic is a crucial part of a house – it can completely ruin your home’s structure and significantly increase the bills you pay each month, depending on how its heat is regulated – or, more accurately, not.

Attic temperature is one of the most underrated things to consider in house-care. Thus, we’ll be discussing it in today’s article for that very reason. What temperature should an attic be? 

The ideal temperature in your attic should be no less than 60 degrees Fahrenheit in the winter and no more than 10-20 degrees hotter than the outside temperature in summer, with a maximum of about 130 degrees Fahrenheit. 

If you can’t manage to keep your attic at these temperatures, it can cause a heap of problems, from simply increasing your energy bills to developing mold that will eat through your house over the years. This is why, even though it’s underrated, more attention should be paid to dealing with this fundamental aspect of a healthy attic: its temperature. Read on to find out more!

What Temperature Should the Attic Be?

Maintaining a stable attic temperature isn’t always the easiest thing to do, but it is an absolute must if you want to keep both your house and your bills in shape. There are a couple of steps to achieving this, the first being to start taking better care of your attic. 

As we answered earlier, when it’s hot outside (70 degrees or warmer), you should make sure your attic temperature doesn’t go above the outside temperature by more than 10-20 degrees, with a maximum of 130 degrees. If it does, this will cause many problems, which we’ll discuss in more detail later on. Just remember the golden rule of staying no more than 10-20 degrees above the outside temperature and act accordingly. 

On the other hand, you wouldn’t want to allow your attic to drop to a temperature below 60 degrees in wintertime. The reason for this is a little different. It’s not because some catastrophe would befall you if the temperatures dropped below that, although you would have trouble heating your house if it was for prolonged periods. Instead, you want to maintain a higher temperature to ensure your heating system can work properly.

Attics are very often looked at as the most unnecessary part of a house. It’s used as “an old warehouse,” and you just throw in things you might need in the future (but never actually use again). This article is for you if this is the case; we will help you realize just how important the attic is. 

If you look at basic physics, you’ll see that hot air rises while cold air is pressed downwards. Once you understand what this means, you can already see the implications your attic might have when it comes to keeping your house in order.

How Hot Should My Attic Be During the Summer?

If the temperature is very hot outside, your attic will be the hottest part of the house. Without proper ventilation, hot air becomes trapped between the insulation and the roof. Ideally, your attic should not exceed 130 degrees Fahrenheit during the summer. Problems related to attics hotter than 130 degrees:

  • It will make it harder to cool your home in the summer. Your HVAC system has to work harder than needed, which leads to premature equipment failure.
  • It can degrade certain types of insulation. Insulation, such as cellulose, is made from recycled materials that degrade over time, reducing the insulation’s effectiveness.
  • A hot attic will cause asphalt shingles to degrade faster, shortening the life of the roof. Asphalt shingles already absorb a lot of heat from the sun. Trapped heat in the attic causes shingles to lose essential oils that protect the shingles.
  • A hot attic can create an environment for mold to thrive, driving thousands of dollars in remediation costs.

How Cold Should My Attic Be During the Winter?

On the other hand, your attic is probably the most exposed part of the house when cold outside. When this occurs, your attic will supply your home with a constant stream of cold air from above without proper insulation, making it hard to keep warm. 

Problems related to allowing your attic to get too cold include:

  • It will make it harder to heat your home in the winter. Your HVAC system has to work harder than needed, which leads to premature equipment failure.
  • If your ductwork is located in the attic, cold temperatures can cool the heat as fast as it is produced. This rises energy costs.
  • Attics that drop below freezing can cause ice dams to form on the roof. These ice dams can cause structure damage under the weight of ice and snow.

Neither of these is situations you want to find yourself in – and that’s just the beginning of what can happen if you don’t pay attention to your attic. So, the first and most obvious question is: what temperature should an attic be? 

Is a Hot Attic Dangerous?

Now, we’ve mentioned that you need to watch out for your heating system’s performance in cold climates, but there are far more problems that might occur due to an unregulated temperature in hot climates. Here’s a breakdown of some of the more important ones. 

As we all know, water evaporates when it’s heated. The same happens in hot climates. It doesn’t have to boil (that’s very unlikely to happen from the hot weather alone), but the heat increases the evaporation of any small amount of water.

For this reason, hot weather tends to be more humid—the problem with humidity in an enclosed space, especially somewhere with lots of wood. Well, you can see where this is leading: mold. A lot of humidity due to unregulated heat and a poor ventilation system (more on that later) is bound to create mold, which will eventually literally eat at the structural elements of your attic and destroy them.

This won’t only cost you money in terms of those wooden planks and other building materials, but it will also compromise the general structural integrity of your home. 

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Another, less likely threat is the one you probably first associated with the word heat: fire. Not all homes are built with quality. Quite a few aren’t. Usually, a poor quality home shows itself in a couple of different ways, such as cracks in the walls due to bad structural and foundation jobs, wet and soggy walls from poorly installed water pipes, etc.

However, in some places in the world, houses can catch fire from the outside heat. This often happens because the attic isn’t properly ventilated or temperature-regulated, increasing the attic temperature to dangerous levels.

In the case of a more open build, where the moisture and humidity can escape, but the heat stays in, some elements can dry out and heat up so much that they catch fire. We don’t need to explain why that isn’t something you would want. 

Do Attics Need Ventilation?

The short and clear answer: yes. However, that doesn’t devote enough respect and attention to this crucial topic. One could even put forward a pretty solid argument that ventilation is more important than controlling the temperature. In this part of today’s article, we will talk about why that’s so. 

In practical terms, ventilating your attic means creating airflow that doesn’t allow humidity and heat to stay in the attic space for long enough to build up. Unfortunately, some houses have attics with absolutely no sort of ventilation. We’ll talk more about the types of ventilation available, but the main thing you should know is that ventilation is necessary for most places when building a new residential home. 

If you’ve bought your home rather than built it yourself and haven’t yet checked whether or not your attic is ventilated, we advise you to do so. Alternatively, call a professional to do so – it might cost you a lot down the line if you don’t. You might not even be aware, but it could have already cost you a pretty penny by significantly raising your utility bills. 

What’s the Best Way to Ventilate Your Attic?

Now, let’s talk about attic ventilation types. There are two main types of attic ventilation systems, called passive and active (sometimes also referred to as powered ventilation). In the next couple of paragraphs, we will go through what these mean and why they are better or worse than the others. 

First, we will talk about basic attic ventilation, which is called passive ventilation. Attic ventilation uses physics to move air in most homes. It consists of two parts: the intake vent and the exhaust vent.

The intake vents are placed at the lowest parts of the attic, under the eaves, where cold air can enter the attic. This cold air literally pushes hot air out the upper exhaust vents (some types include turbine vents, ridge vents, or roof vents) located near the top of the roof or the ridge.

Passive attic ventilation is best because it:

  • It uses physics to move air inside the attic.
  • It uses no mechanical energy to move hot air out of the air.
  • It requires no human activity to vent the attic.

Active systems, on the other hand, rely on some form of ventilation fans. What this does is nothing more than speed up or force the same process of the passive system. There isn’t much more to be said about active systems since it’s the same concept but with a machine to help. 

Active systems require:

  • Ventilation fans require electricity to power the fans.
  • Ventilation fans need to be replaced about every 15 – 20 years.
  • Ventilation fans have thermostats that have to be set and maintained.

One exception now on the market are solar-powered ventilation fans. these fans use self-generating power with built-in thermostats making them virtually effortless.

One of the best rated solar-powered attic fans I’ve seen in use is the Solar Attic Fan with Thermostat/Humidistat – Brushless Motor – Hail and Weather Resistant Solar Vent Fan – by Remington Solar

However, a home can have active and passive systems that can be combined – and usually are. Take a passive intake vent and an active intake fan, then put these two work together to draw colder air into the attic. You can then either add a passive vent, like a ridge vent, or an active exhaust fan, such as a vent fan, or a combination of both in intricate roof designs. You can combine these in any way that works most productively for your attic. 

Many people consider the active systems a waste of money since they don’t do much of a better job than the passive systems unless you pay a nice sum. For this reason, passive systems are generally more recommended and more common than active systems. 

What Temperature Should an Attic Fan Be Set at in Summer?

Some types of higher-end active fan systems combine temperature control and ventilation into one. If you’re planning on installing one of these systems – or perhaps already have one of them installed – you might be thinking, what’s the optimal temperature to set the fan at? 

Contrary to intuition, you should set your attic fan in a hot climate at a temperature between 90 and 110 degrees. Most attic fans have a thermostat that signals the fan to turn on and off once the attic reaches a specified temperature.

Since you don’t want your fan going all the time due to utility costs and the system’s lifespan, the best option is to set it to a temperature that isn’t extremely hot but hot enough that your fan isn’t always on. 

You can also set up a humidistat, which can measure the humidity levels in your attic and turn on the fan when the levels reach a certain limit, regardless of temperature. A humidistat helps prevent mold and other moisture-related issues by also turning on when humidity levels reach the designated humidity level since it doesn’t take ridiculously high temperatures for a lot of humidity to build up in the attic.

Suppose you have your fan set to 100 degrees, but your attic’s internal temperature stays near 90 for prolonged periods. In that case, that’s still more than enough for humidity to begin to affect your attic. 

Should You Use Radiant Barriers in Attic?

Radiant barriers add a layer of insulation and work by reducing radiant heat energy transfer from one side of the barrier to the other. Although this is generally considered useful in most places, it’s an incredibly productive choice if you happen to be living in a warmer climate.

Some studies show that radiant barriers in the attic can cause a decrease of up to 10% in utility bills in particularly hot climates, associated almost exclusively with keeping temperatures down. This can be quite a significant difference over time. 

So why does this work? Radiant barriers are made up of a material that doesn’t transfer heat easily. This way, the heat coming in from the Sun won’t heat up the attic air as much as it would otherwise since there’s an extra layer of insulation in place. Radiant barriers work better when the temperature difference on the two sides of the barrier is greater, which is usually the case in summer. 

So, in short, yes, radiant barriers do help, but especially in warmer climates. However, if you do happen to be living somewhere colder, then it might just be an added expense that doesn’t help as much as it could. The best choice is always to consult a professional, as they can evaluate your home and will know exactly what they’re talking about. 

Many new construction homes are built with radiant barrier OSB wood sheathing that combines a radiant barrier and roof sheathing into one step. Radiant barrier OSB sheathing can be installed during the roof replacement, but it requires removing all existing roof decking to install the radiant decking.

Replacing existing roof decking with radiant barrier roof decking is often costly, and studies are inconclusive as to the full benefits long-term. According to energy.gov, in existing homes in cold climates, “it’s usually more cost-effective to install more thermal insulation than to add a radiant barrier.”

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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