Tag Archives: ventilation

Controlling Humidity in your House

Controlling humidity in your house is important for several reasons.  Comfort is one reason, but preventing rot and mold is likely more critical.

A pretty picture but does not have much to do with controlling humidity
Ian Sane / Foter.com / CC BY

In cooler climates moisture must not be allowed to pass through the walls from the inside to the framing and insulation. Humid air will condense in the wall space and create conditions for mold and rot. In extreme cases, insulation can become saturated, or even frozen into a solid block.

The usual solution is to provide a moisture proof barrier under the interior finishing board. This is usually 6 mil polyethylene. Extra care must be taken to seal against all possible leaks. Electrical and plumbing penetrations are common problem areas as well as laps in the poly.

The Icy Explosion
Stuck in Customs / Foter.com / CC BY-NC-SA

Moisture escaping into the attic can form frost on the underside of the roof. When the weather warms this will melt and can saturate insulation and stain interiors. Good attic ventilation can help to clear moist air that may escape into the space but the poly barrier is the best solution.

Moisture can also condense on inside walls and create an environment for mold. This often happens behind furniture on north walls. Areas with inadequate insulation also create a problem. Forced air heat often does not reach into closets and behind obstructions, hindering drying. Under floor radiant heating is better in this regard. Diagrams of simple radiant systems can be found here.

Too little indoor humidity is not a huge problem but you may be more comfortable if it is maintained at 50 to 60 percent. Older houses with substantial air leakage can have a very dry interior environment in cold weather and a humidifier can add comfort. Too dry air can cause static electricity and dry throats.

controlling humidity can prevent undue window frost
Pretty but can be a problemmonteregina / Foter.com / CC BY-NC-SA

Modern houses are normally well sealed and the opposite often occurs. Moisture added from bathrooms, cooking, laundry and even occupant respiration can raise humidity. Attached garages may add humidity from wet cars or snow and ice melting from car undersides. Un-vented gas cook stoves add considerable humidity as a by-product of combustion. Too damp an environment can cause mold growth and windows may frost up in cold weather. Damage can occur when this frost melts. I have even seen door locks freeze solid and become inoperable.

In cold drier climates the best solution is ventilating with outside air. A heat recovery ventilator keeps heat loss to a minimum. This is the method I use in my house. It has the added advantage of replacing stale air with fresh and reducing odors. So far it has been easy to maintain humidity to between 50 and 55 %.

Many contractors will install complicated ventilating systems with many inlets and outlets. I do not think this is necessary and could be very difficult to balance. One or two well placed inlets and one or two outlets should be adequate for most houses. You should also install bathroom exhausts and a kitchen range hood that exhausts to the outside. You may need a separate make up air inlet for these. It is a good idea to wire the bath exhausts to turn on with the light. People will often forget to turn fans on when needed.

You won't need this large a fan for controlling humidity
Foter.com / CC BY-SA

Ventilators are usually controlled by a humidistat. You may at times want to control it manually to provide fresh air.

You may need a de-humidifier in humid climates or in especially damp basements. Air conditioners normally reduce indoor humidity in hot climates. Humidity makes hot weather much more uncomfortable. The ability of your body to cool itself by sweating is impaired by high humidity.

Most ventilators available today are probably a little larger than is needed for a smaller house. A smaller unit run more or less continuously may be a better answer.  The one in my house is quite large but does not create any real problems except for a slight draft when it is running. Not much of a problem as the moving air is not cold.

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Systems make a house work

Your home is a system in itself, but there are several other systems that are an integral part of the whole.

These include, but may not be limited to an electrical system, plumbing, heating, air conditioning, ventilation, communications and security. Each has to be considered, and planned for, when you build your new home. The overall building envelope is a system as well, although a passive one.

The electrical system is perhaps the most important to the functioning of your home.

electric system
K.G.Photos / Nature Photos / CC BY-NC-ND

Virtually none of the other active systems can operate without it. When planning your electrical system, you must consider all the other systems that will rely on it. One of the first steps is to determine the load you will be placing on it. This link will take you to a table showing the typical demand of common household equipment. Remember, that not every item will be in service at the same time. A cabin or outbuilding may get by on a 60 or 70 amp service rating. Allow for at least 30 circuits. With a small house a 100 amp service is probably adequate. Large houses will need at least a 200 amp service. Local codes may not allow the lowest ratings in a house.

Most of your circuits will be 15 amp at 120 volts. Some higher amperage and voltage circuits may be required for kitchens, heating appliances, ranges and dryers. Most codes now require arc fault beakers in circuits that include bedroom receptacles. These are expensive, so plan your bedroom wiring to minimize the number you will need.

transportation and electric systems
kevin dooley / Car Photos / CC BY

When planning, do not forget to allow for extra plugs for office or computer areas. Allow for service to air conditioners, furnaces, ventilators, and exhaust fans. Don’t forget your sump pump. If you are installing a hot water circulating pump it will require electricity. You might want to provide a plug for an electric welder in your garage.

Codes may only require one outlet in a garage, but I find this a little ridiculous. I usually plan for many more. Wire for garage door openers, even if you do not plan to install them immediately. Under eave plugs are handy for Christmas lights.

Codes often call for only one outdoor plug, but I think you will appreciate more, one at the back as well as one at the front. Larger houses should have more. Only the one needs to have a separate circuit, but all need to be GFIC. Don’t ignore the deck or patio area. Plan for sub services that may be needed, such as for a detached garage or other outbuilding. Allow for your security system.

Wiring for low voltage applications, such as door bells and thermostats, needs to be planned. If you are off grid, or planning to supplement your electricity usage with solar or wind, things become considerably more complicated and beyond the scope of this article.

Electrical wiring diagrams and explanations. link

communication system
Helga Weber / Foter.com / CC BY-ND

Your communication systems need wiring as well. Plan possible satellite dish locations, land line connections, and possible radio antennae. Once again, don’t neglect office, entertainment or computer areas. Doubled runs of both category 5 telephone cable, and the best quality co-ax cable is a good practice. It is best if each run originates in a distribution box, similar to your electrical wiring. Perhaps you will want speaker wiring to different parts of your house or to the patio.

Security systems can be done by wireless, but permanent wiring is a little more dependable, and requires less maintenance. You may need low voltage wiring, a house wiring connection and video cable. Plan the location of surveillance cameras, motion detectors, monitors and telephone connections. Be certain that control panels will not be visible from windows.

Plumbing systems brings you fresh water and removes waste water. While not as complex as your electrical wiring, the possible designs are not quite as flexible. Getting the water to your various appliances and fixtures is fairly straight forward. For the most part you simply have to get it there in sufficient quantity to do the job. There are two sides, the hot water and the cold. Decide if you wish to use a circulation system on your hot water. Familiarize yourself with the codes pertaining to hot water safety.

plumbing system
Pixelicus / Travel Photos / CC BY-NC-ND

Your main plumbing runs will be ¾ inch pipe to start and reducing to ½ inch. A good method is to use a ¾ inch manifolds and run ½ to each application. Don’t run ¾ to far from your water heater, if it isn’t part of a circulation system, or it will take too much time to get hot water to the application. This wastes water and energy.

Plan for a cold connection to your refrigerator and toilets, and a hot one to the dishwasher. Pex or copper piping is commonly used today. Sizes are inside diameter. Metric conversions are 13mm and 19 mm for ½ and ¾ inch respectively.

Don’t skimp on valves to isolate applications or components of your system. They make repairs and replacements much easier and less disrupting.

Waste water installations must follow rules of physics as well as health and safety regulations. All connections require traps and venting to prevent sewer gases from entering the house. Plan for clean outs at the bottom of each vent stack and at 90 degree turns. Special methods are needed to vent a sink or dishwasher located in an island cabinet. Provide for drains on high efficiency furnaces and air conditioner coils.

Codes may require a device to prevent back flow where the sewer exits the house. It is a good idea in any case.

For wastewater, ABS or PVC pipe is commonly used in sizes from 1.25 to 4 inches (32 mm to100 mm).

Many jurisdictions will not allow a sump pump connection to the waste water system. A provision will have to be made to connect to a storm sewer or to daylight.

Plumbing basics link

ventilation system
reinvented / Foter.com / CC BY-NC-SA

I have covered heating systems in a previous article that I have linked to here. Plan the locations of your warm air vent and the cold air returns for the best distribution pattern if using a forced air system.

Modern tightly sealed houses require ventilation for maintaining air quality, and for humidity control in many climates. Heat recovery ventilators can be a good investment in cold climates. Allow for the locations of vents, ducting, and for the ventilator itself. Exhaust fans will be required in the kitchen and bathrooms to vent excess moisture and odors.

How to get the ventilation you need in your house. link

There are minimum clearances required between exterior terminations and service connections as well as between outlets and inlets.

If you do not use forced air heating, then you may need ducting for air conditioning. A ductless mini-split system is an alternative, but allowances may have to be made for drains.

I have only briefly covered the active systems in a house in this article. It is primarily meant as an aid to planning, but I will try to get into more detailed discussions of each system in future posts.

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Attic ventilation a critical design factor

 Attic ventilation and insulation is critical to reduce cooling costs, to prevent shingle damage, to minimize ice damming, and to prevent moisture buildup. Installation is not complicated.

An unvented attic is like a politician or me—–full of hot air.

If the area directly under your roof does not have adequate air movement for cooling, the sun can raise temperatures to levels damaging to asphalt shingles. Heat is also transferred to the living space below, and increases cooling costs. In the winter, heat rising through the ceiling to a poorly vented attic space can melt snow on the roof. The resulting water can run downward, and refreeze on colder areas of the roof to form ice dams. The water pooling behind the ice dams can overwhelm the roofing and leak through. This will cause severe damage to insulation, ceilings, and interior decorating. Excess humidity needs to be removed from the attic space to prevent damage to the roof and insulation from mold and rot.

Attic ventilation

Types of attic vent

In one severe case, I saw where asphalt shingles badly curled in 5 years. They normally would not have been as bad after 20 years. This was a shed type roof on an addition to the south side of a two story house. The shingles were black. The wall above was painted white, reflecting heat onto the roof, and a wall opposite was also white, reflecting heat back again. The original cedar shingle roof had been removed, and insulation had been stuffed in from the top. No attic ventilation of any kind had been provided.

Admittedly, this is an extreme example, but it serves to demonstrate the importance of attic ventilation.

Complicated roofs can complicate the equation considerably, but adequate ventilation on a simple gable roof is not difficult to achieve.

A continuous ridge vent combined with vented soffits is a low maintenance passive system that works well. Ridge vents should not be combined with other types of vents in snow areas, as snow may blow into the attic. There is much less chance of serious leaks with ridge vents.

In older houses, the 3” x 10” screened vents about every 4 feet in the soffits combined with one or two square vents near the ridge, is not really adequate.

I believe that passive attic ventilation is a better option for attic ventilation than powered fans, or systems with moving parts. It is dangerous to be on the roof to affect repairs when there is snow. Working on the roof in hot weather can damage asphalt shingles. There can be noise problems. Power outages render fans useless. Electricity consumption is a cost, and an environmental concern.

A complicated roof may require more complicated solutions. Vaulted ceilings make insulating and venting difficult, as do attic living or storage space. Of course, this is another argument for simpler roof designs.

There are minimum requirements in building codes for attic ventilation, but once again I advocate going a step further, and providing somewhat more.

Care must be taken to not block the attic ventilation at the eaves when insulating. Insulation stops will be needed in many cases.

There are a great many attic ventilation devices on the market.

Most require a hole through the roof which means they may leak, if not properly installed, or if they become damaged from wind or hail. Made of metal or plastic, they are usually obvious, and not necessarily attractive. Most will work fairly well, if there is enough of them, and they are well placed.

Gable vents seen on older houses are not that effective, due to poor air distribution.

Turbine vents are popular, but I really don’t think they are much more effective than static vents. They can be noisy, and more so if they are damaged by wind or hail.

Power vents can move a lot of air, but care must be taken to provide extra inlet vents, if they are to be any more effective. Distribution of air movement may not be that even. Their true effectiveness is arguable. Solar powered models are available to reduce energy cost and eliminate wiring.

For cost and effectiveness, I believe that ridge venting with vented soffits is the better option for attic ventilation. It works the best on a gable type roof. If you choose the type that you shingle over, it is virtually invisible from the ground. Some other roof designs will require different solutions.

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