Condensation on inside of windows

Great post by Oberon on  - http://www.doityourself.com/forum/doors-skylights-windows/362701-condensation-inside-windows.html

Okay, it is that time of year - here is the really long version!

You have interior condensation on your windows simply because the surface temperature of the window is below the dew point temperature of the air in your home…that’s it…a very simple explanation.

Unfortunately, as to why the surface temperature of your window (glass) is below the dew point temperature of the air in your home may be a bit more complex – so I am going to offer a few thoughts and maybe even throw in a few numbers that I hope might help your situation.

In the summer, when you pull something cold and refreshing out of the refrigerator, and the air is warm and humid, that cold and refreshing beverage container suddenly and quite magically becomes instantly wet – just as soon as it is exposed to the air. What has happened is that the temperature of the container fresh from the refrigerator is below the dew point temperature of the air – which has caused condensation on the outside of that container.

What happens to your windows in the fall and winter is that the surface of the glass is below the dew point temperature of the air in your home – which is causing condensation on the surface of that glass.

Dew point is defined as saturation vapor density...or put in simpler terms, when the air reaches 100% relative humidity and can hold no more moisture.

Relative humidity is, well, relative.

Relative humidity is a comparison of the actual vapor density versus the saturation vapor density at a particular temperature. Put a bit more simply, dew point is 100% relative humidity or the point where the air - at that temperature - is no longer able to hold any more moisture. If the air has reached vapor saturation (100% relative humidity), then the air will release moisture...be it on the outside of that cold beverage container in the summer time, or be it on the interior glass surface of your windows in the winter time, it makes no difference. If the surface temperature happens to be below freezing, then that moisture becomes frost or even ice.

In order to stop condensation from forming on the surface of a window, you either have to lower the dew point temperature of the air in your home to a level below the dew point temperature of the window surface, or you have to warm up the window surface to a temperature above the dew point temperature of your home, or a combination of both.

Lowering the relative humidity of the air in your home may have absolutely no effect on controlling window condensation or it may completely solve your problem – depends on how you lower the relative humidity and what affect the “how” has on both the moisture level of your air and the temperature of your windows. All this because there are two ways to lower relative humidity – first, you can increase the air temperature in your home or second, you can decrease the moisture content of the air in your home.

By increasing the air temperature in your home you will lower the relative humidity but you will not change the dew point – which is based on the amount of water vapor in the air and is not based on the temperature of the air. So, while the RH is lower with higher air temperature, it may not effect condensation on window surfaces at all – unless the rise in air temperature also caused a corresponding rise in window glass temperature to a level above the dew point temperature.

But, lowering the amount of water vapor or moisture in your air will lower the dew point temperature as well. And if it lowers the dew point temperature sufficiently to drop it below the temperature of your window glass – no more condensation issues.

The amount of moisture in the air is measured in grams per cubic meter, which is kind of nice for our metric folks but not so nice for our non-metric folks; but the metric version is much easier on the calculator than the English version. However, in the interest of making this stuff easier to understand for all of us non-metric types, I am going to use Fahrenheit rather than Celsius temperatures in the calculations.

Okay – consider your home at 65 degrees F and with a relative humidity reading of 40%. There are 6.25 grams of water in a cubic meter of air in your home in that particular scenario - which then equates to a dew point temperature of 38 degrees F. So at 38 degrees the air will be at 100% relative humidity or at saturation vapor density.

Now, if your neighbor keeps her house at 75 degrees, but she also has 6.25 grams of water per cubic meter in her air, then the relative humidity in her home is 29% - versus your 40%. But, and here’s the kicker, the dew point temperature in her home is still 38 degrees.

While the relative humidity in her home is much lower than is the relative humidity in yours; if the surface temperature of the windows in her home is 35 degrees she will have condensation on those windows…yet if the surface temperature of your windows is 40 degrees – only five degrees warmer – you will not have condensation on your windows.

So, while her handy humidity gauge reads (correctly) only 29% RH – she has a condensation problem.
While your handy humidity gauge reads (correctly) 40% RH – you don’t have a condensation problem…SWEET…well, for you anyway, not her.

If your home hygrometer measures the relative humidity in your home at 60% while the temperature of your home is 70 degrees, you will have a dew point temperature of about 51 degrees – meaning that if the temperature of the window surface is below 51 degrees then you will have condensation - so now we talk a little more specifically about windows.

The interior surface temperature of a single lite of glass, when the temperature outside is 0 degrees F and the inside air temperature is 70 degrees, will be about 16 degrees.

Add a storm window on the outside and the surface temperature of the inside lite jumps up to about 43 degrees – a huge improvement.

But these are center-of-glass readings and not the temperature readings at the edge of the window where condensation usually forms. A typical clear glass dual pane window is going to have center-of-glass temperature reading pretty much the same as a single pane with a storm – however, if that dual pane has a LowE coating and an argon gas infill then the center-of-glass temperature will be about 57 degrees – a 14 degree improvement over a clear glass dual pane or a single pane with storm window – but again, and more importantly, there will be a comparable edge of glass improvement as well, particularly if the IGU (Insulating Glass Unit) was manufactured using a warm edge spacer system. Also, the dual pane is going to have desiccant between the glass layers. Desiccant absorbs moisture keeping the inside of the dual pane system very dry.

The advantage? If it gets cold enough outside, the temperature in the airspace between the lites can get very low. By keeping that space dry, it helps to keep the dew point temperature very low as well; something not always possible when using a single pane and storm window.

Oddly enough, a single pane with a good and tight frame and sash assembly may be more prone to condensation than will a less tight single pane window simply because air (and moisture) will leak out of the looser window while the tighter window may be more likely to trap the moisture inside the home. And, while a tight storm window can help the interior lite to avoid condensation (when compared with a single lite and no storm), the storm window itself may frost up when the temperature is low enough – at a temperature usually well above the temperature that will cause the dual pane to ice up. It is unavoidable given the right circumstances

So what does a window temperature of 57 degrees mean? Well, as I mentioned earlier a home kept at 70 degrees with a 60% relative humidity has a dew point temperature of 51 degrees so it is much less likely that there will be condensation problem on those particular windows than there would be with a less energy efficient window - despite the relatively high relative humidity in the home.

But, there is always a "but"…

Again, that 57 degree glass temperature is still a center-of-glass reading and the edge of glass temperature will be lower - actual temperature is dependent on both the spacer system used in the IG unit construction and on the material used to construct the sash. So even with a "57 degree" center-of-glass temperature it is still possible to get window condensation if there is enough moisture in the air.

And consider that the interior glass temperatures are based on the fact that moving, warmer, indoor air is actually in contact with the glass at a given time. Curtains, shades, other obstructions can cause problems by blocking airflow across the glass – airflow that can have a huge effect on the condition of the window relating to condensation. Also, bay and bow windows can be more prone to condensation – again because of the possibility of decreased airflow over the glass.

And finally, what can happen to the dew point if you keep your home at 70 degrees and you have a 65% relative humidity? Well, for one thing the dew point has jumped up to 57 degrees which we have already noted is the same as the window temperature. For another thing, anyone with 65% relative humidity in a home at 70 degrees has way too much moisture in their air and they are in serious need of some sort of ventilation system – or at least several good exhaust fans!

Read more: http://www.doityourself.com/forum/doors-skylights-windows/362701-condensation-inside-windows.html#ixzz3MHiQZZ5x

Scarf joint rotten floor joist ends in Finistere, Brittany.

How to scarf joint rotten floor joist ends?

In the process of renovating our new home, we noticed one of the gable walls was suffering from Damp. After tracing back, looking for the cause I came across a few joists which had rotten ends. The damp patch on the wall was due to a leaky gutter, allowing water to penetrate down the wall on 2 levels and working its way round the corner stones, thus the damp patch.

After rectifying the gutters, next on the game plan was to fix our rotten floor joists ends.

This subject is as broad as it is wide. Online, you'll find many options as well as different methods of resolving this problem. I'll explain which method of resolution we chose as well as how I executed the fix. This job will not be for everyone but worth being aware of.

In our scenario, the floor joist reside in a street level, north facing room. The room below  is basement level, no windows, and granite dry stone walls. The basement room does suffer from severe humidity which is another topic to talk about in the future.

The street level room has a thin cut solid chestnut tongue and groove flooring. With these environmental ingredients, I knew I didn't want to remove the flooring, experience has told me that French chestnut floors are a pain to remove due to their secret nails and expensive to replace. Using metal hangers with nails would encourage condensation and cause further damage in the future.


As the property is of a traditional build, not wanting to use anything metal and wanting to carry out the fix on the cheap (one after another unexpencted gremlins all mounts up), I chose to go the old school route and use a nibbed scarf joint.

What is a nibbed scarf joint I hear you cry what were the alternatives?

A Scarf joint is; "Over to you Wiki" -

A scarf joint (also known as a scarph joint) is a method of joining two members end to end in woodworking or metalworking.[1] The scarf joint is used when the material being joined is not available in the length required. It is an alternative to other joints such as the butt joint and the splice joint and is often favored over these in joinery because it yields a barely visible glue line.
 - http://en.wikipedia.org/wiki/Scarf_joint

For this incidience the rotten joist end were cut off and an angle cut is made to bottom of the beam to allow a new part to be bolted (or dowled) on a good distance from the fulcrum point. As stated before it’s a traditional repair, low cost and can be finished to match the original joist.

The alternative methods are -

Joist Repair Plates

Basically using two "L" section steel, slide in the the joist footing well and farsen to the good part of the joist.


Resin Slice Joist

The rotten end of the beam / joist is cut off.  A vertical slot is machined in the joist.  A new joist end is drilled to so two or more steel bars can be glued (Resined) in.  The new end is then fitted with the bars going in to slot. Resin is then poured in to the slot to secure the new beam end. (This looks to be a pain in the ass!)


Replace the whole joist. hmm, I wouldn't want to do this on my tod!


Last option is only viable if you have a run of end joists to repair - Using Hangers.

This picture says a thousand words, though I have noticed they used screws. This is not advisable as the screw heads can and will rip off!



Positives with using a scarf join (Nibbed/Vee'd ends) -
Its cheap
Looks good
Can be done without the use of metal.
The finished flooring doesn't have to be removed in you have access from the underside.

Negatives -
Difficult to cut in situ, up a ladder upside down. Difficult to set out and accurate craftsmanship required.
Quite a few tools required compared with the other methods


How is it done and the method I followed.
Obviously for the benefit of this project I have simplified the procedure... But not by much! It really is an uncomplicated breakthrough allowing new, treated timbers to be installed with the minimum of fuss and disturbance.
Timbers are not all accessible from the same place. While you may be able to get to a floor joist from the top by lifting a section of the floor, it is far easier to access a rafter from underneath.

In the below sequence of images I  have shown the most basic, repairing a floor joist that is accessible from the basement level. 

(Setting out the cut.)

 

(Cut Vertically to the diagonal line.)

(Cut along the setting up lines.) 

 (Chisel, plane & sand till its perfectly flat.)

 (Make a left & right template and map out onto replacement timber.)

(Position, fix using dowel, 90degrees from the diagonal.)

 

Conclusion:

In fairness, this isn't the easiest of jobs. I would've preferred using hangers from an ease point of view. Though more material would have been required, all you would have needed is a saw, and a hammer.

 

"NEXT!"